Door hardware on commercial sites can look simple from across the hallway: a latch, a access control systems and software door, maybe a card reader. Up close, the “how” matters. Door interlocks, strikes, and magnetic locks are the parts that decide whether a door releases on demand, whether it stays shut when it should, and whether two doors coordinate safely. This article gives you a practical overview of what these components do, how they differ, and what to watch for when you are specifying, troubleshooting, or coordinating an install.
The cast of characters: who does what
It helps to separate the functions. A lot of field confusion comes from people using the same word for different layers of the system.
A strike is the mechanical interface between the door and the frame. In plain terms, it is the part the latch engages. Depending on the style, a strike can be purely mechanical, or it can be electrically controlled so the latch can release when you command it.
A magnetic lock, often called a mag lock, is an electromechanical device that holds the door closed using magnetic force. When power is present (or absent, depending on design), it either locks or unlocks. Many mag locks are used with access control and electric strike systems in the real world, but they are not interchangeable.
A door interlock is the coordination logic between doors, typically in pairs, so that the doors cannot be opened at the same time in a way that compromises safety, pressurization, or security. Interlocks can be purely mechanical, but on most access controlled sites they are implemented electrically with control wiring and sometimes a controller.
Once you see those as distinct jobs, the rest becomes clearer: strikes and mag locks handle “release and hold,” while interlocks manage “when release is allowed across doors.”
Door strikes: electrically controlled latch control
A typical electric strike (or electrified strike) sits in the frame where the latch normally hits. The electrical portion controls whether the strike presents resistance to the door’s latch. When energized, many strikes allow the latch to retract and the door to open. When de-energized, the strike may revert to locked or unlocked depending on the fail state.
The big practical point is the fail condition. Most people remember “fail safe” and “fail secure” as slogans, but you feel the difference immediately when power drops.
- A strike configured for fail safe behavior will typically release on loss of power, supporting egress in an emergency power interruption scenario. A strike configured for fail secure behavior will typically stay locked on loss of power, favoring security but changing how you must handle life safety and emergency requirements.
In the field, the “fail” choice is not just an engineering preference, it is part of code compliance and site policy. If you are working on a retrofit, the existing fire alarm interface and egress strategy often determine what is allowed.
A quick lived example
I once walked a building where two offices had the same door type, same brand of hardware, and nearly identical access control panels. One door worked perfectly. The other door would occasionally not unlock for staff after a scheduled test. The cause was mundane, not mystical: the door that failed had been wired with the strike control polarity swapped during a tenant improvement, so the strike logic responded opposite to the command. The system still “looked” correct at the panel, until you traced the actual voltage behavior at the strike during a test sequence. That is the sort of thing that makes strikes feel simple until you measure them.
Mag locks: magnetic holding force and how it behaves
Magnetic locks use an electromagnet plus an armature plate on the door. Power provides the magnetic field. When the field drops, the door can open, provided nothing else is preventing the latch from moving.
Mag locks are popular because they can be relatively straightforward to integrate with access control and because the visible hardware on the door surface can be minimal. They also pair well with certain door and frame conditions where a traditional mechanical lock might be more invasive.
But mag locks come with their own set of details:
Holding strength is not the whole story. The magnet rating tells you about holding force, but door alignment, frame flex, and strike gap all influence real performance. Residual mechanical factors matter. Many mag lock installs still require a latch or keeper that prevents the door from pulling open under load, especially where there are air pressure differentials or high traffic. Temperature and power supply behavior can influence performance. If a power supply is undersized or has voltage drop across long runs, the lock may not reach full holding force.Fail safe vs fail secure with mag locks
Mag locks are commonly sold and installed as either fail safe or fail secure based on whether the magnet needs power to hold. You also have to consider how the fire alarm system should interact, particularly on doors that must release during a fire alarm or power loss.
From a troubleshooting perspective, you can often narrow down mag lock issues quickly by looking for the classic symptoms:
- Door unlock requests that do not produce any movement Persistent “locked” states after card reader events Doors that unlock during testing in ways that do not match expected logic
In most sites, the root cause is one of the following: wiring, power supply voltage drop, an incorrect trigger type, or the door contact being out of adjustment and never reporting the state that the controller expects.
Interlocks: coordinating two doors so the system behaves as a system
If strikes and mag locks handle the “holding,” interlocks handle “mutual exclusivity.” The classic application is a vestibule setup where two doors face each other. The goal is to prevent both doors from being open simultaneously, which can undermine security and, in some environments, disrupt pressure zones.
Interlocks also appear in settings like:
- Controlled entry points where you want a specific traffic flow pattern Areas with high-security requirements where two openings should not be simultaneously accessible Scenes where you need to prevent cross-contamination risk between spaces, at least from an airflow standpoint, depending on the design
An interlock system can be built around a dedicated controller, a lock controller with interlock logic, or relay logic depending on the complexity and the site’s existing infrastructure. Some interlocks are “hardwired” to enforce physical constraint, while others are “software enforced” through access control rules. In practice, the most robust designs use both: reliable hardware logic plus controller state verification.
The most common interlock failure mode
When interlocks go wrong, you usually see one of two flavors:
- Doors refuse to release when they should because the controller believes the other door is still open or unlocked. Doors release in unintended combinations because the interlock contact logic is inverted or because a door position sensor is not providing reliable feedback.
The lesson is that interlocks depend on accurate input. Door position contacts, request to exit signals, and status feedback must all align with the logic you think you implemented.
How these components work together in real systems
Most installations are not “one component only.” They are a coordinated chain. For a typical access controlled corridor with a door pair, a scenario may look like this:
- Card reader or keypad grants an unlock request for door A. The controller checks door A’s state and confirms door B is not open. The controller commands the strike or mag lock on door A to release. A door position sensor verifies that door A moved appropriately, then the system updates status. The interlock logic prevents granting door B access until door A has returned to a safe state.
Where this becomes tricky is when you add fire alarm integration, request to exit behavior, and override modes like “door held open” or “after-hours free egress.” Each of those events affects the interlock state machine.
Trade-off: security logic vs life safety behavior
A design that is strongly security driven might prefer fail secure behavior, keeping doors locked when power drops. Life safety systems often require doors to release under specific emergency conditions. That means the final design is rarely a single choice, it is a set of coordinated interactions with fire alarm outputs, power interruption strategies, and sometimes additional hardware like door hold open devices or electromagnetic releases.
If you are specifying hardware, do not treat the access control logic as the only driver. Coordinate with the fire alarm and the door egress requirements early, because once doors are built out, changes to wiring paths, power supplies, or fail states can be expensive.
Choosing between a strike and a mag lock: what you should actually evaluate
People often ask which is “better,” but that is usually the wrong question. Better for what conditions, what door construction, what compliance requirements, and what maintenance tolerance.
Here is the evaluation that tends to matter on actual projects:
- Door and frame geometry: If the door-to-frame alignment is inconsistent or the gap tolerance is tight, a magnetic lock installation might be sensitive, or you might have to add mechanical supports and shimming. Mounting surfaces and wiring paths: Some frames are already prepared for strikes. Others require brackets and field work for mag lock armature placement. Maintenance and long-term reliability: Electrified strikes generally have fewer moving parts than a purely mechanical solution, but they still require correct alignment and periodic checks of latch and strike engagement. Mag locks are also robust, yet they rely on good surface contact and stable power. Power supply and wiring design: Both systems require reliable power. Mag locks can draw higher current depending on model and holding force. Voltage drop and wire gauge selection can be a deciding factor. Integration with controls: If your access controller already has outputs for electrified strikes with supervision, you may have an easier integration path.
A practical comparison that keeps you honest
Here is a concise way I’ve seen teams align internally when the scope includes access control and door status feedback.
| Component | Typical job | Strong fit when | Things that bite you | |---|---|---|---| | Electrified strike | Releases or retains latch engagement from the frame | You want a clean latch interface and frame-friendly mounting | Wrong fail state behavior, latch misalignment, insufficient strike engagement | | Mag lock | Holds door closed using magnet force | You want minimal door surface hardware and flexible mounting | Gap tolerances, power supply voltage drop, poor alignment between magnet and armature | | Interlock | Controls which door can unlock based on other door state | You need vestibule coordination or mutual exclusivity between door pair | Door contact wiring polarity, stale status inputs, logic conflicts with exit modes |
Wiring, supervision, and what to verify before you call it done
Even when hardware selection is correct, installations fail on verification. The “quick overview” version of the truth is that success depends on supervision wiring and testing behavior under realistic conditions, not just a first power-up.
Many access control systems support monitoring of lock status, request to exit contacts, door position contacts, and sometimes current draw on powered devices. When supervision is used, the system can alert you when something is off, like a stuck contact or an open circuit.
Two checks that save hours during commissioning
You do not need a long list to get the value. During commissioning, I recommend you build your verification around observation and measurement.
1) Confirm fail behavior by simulating power loss or command states, based on what your fire and emergency plan requires.
2) Confirm the door position input changes when the door moves, not when it is expected to move.That second point sounds obvious, but I have seen installations where the magnet strength was plenty, yet the door never reported open because the door contact was mounted in a spot that never saw the magnet actuator travel far enough.
Common edge cases that show up in the field
Door prop and latch engagement issues
Even with the best electric hardware, doors can behave oddly when users prop them, slam them, or do not let them close fully. A strike-based system often depends on the latch catching cleanly. A mag lock system often depends on consistent gap and correct alignment.
If the door is not fully closed, the latch may not engage, or the controller may never see a “closed and latched” condition. That can break interlock access control companies logic, because interlocks often depend on door state signals.
Request to exit versus access granted
Most facilities allow egress even when access control otherwise restricts entry. The controller logic usually treats request to exit differently than card access events. If the interlock logic does not account for request to exit mode, you can get situations where door A refuses to release because the system still believes door B is “open enough” to block it, even though request to exit is active.
This is why a commissioning plan should include both normal access events and exit events, especially during after-hours modes.
Fail state mismatches during renovations
Renovations are where you can inherit old wiring practices. The most expensive mistakes usually come from mixing existing devices with new ones without confirming fail state and wiring conventions.
If you are replacing a strike or mag lock on a live system, get clear on how the existing controller output is meant to operate: energized means locked, de-energized means locked, or vice versa. Then confirm at the device level, not only at the panel.
A simple commissioning checklist you can actually use
When you are standing at a door pair and you want to know whether the system will hold up under daily use, you can follow a short process. It should not take long, but it needs to be deliberate.
- Verify the fail state for the strike or mag lock against the project requirements and how the fire alarm interface is supposed to behave. Confirm door position sensors report correct “closed” and “open” states during controlled opens and closes. Test interlock behavior by requesting unlock on door A while door B is open, and then again with roles reversed. Measure or check power stability if the mag lock is involved, especially if cable runs are long or shared.
That list is short because the goal is clarity. The important part is consistency: run the same tests the same way, so you can compare doors and spot the one that is wrong.
Troubleshooting patterns: what to check first
When something fails, do not start with replacing parts. Start with narrowing the problem to either control logic, device physics, or wiring and feedback.
A useful mental model is to ask three questions in order:
Is the controller commanding the correct output? If not, you have logic or configuration problems. Is the output actually reaching the device with the expected voltage or activation state? If not, you have wiring, polarity, or power supply issues. Is the device doing what physics requires and does the system receive the expected feedback? If not, you have alignment, contact mounting, or status wiring issues.If you follow that order, you avoid a lot of random swapping. It also makes it easier to communicate with electricians, low voltage techs, and building owners, because you can describe the failure as “command correct, device not responding,” or “device responding, but door feedback not changing.”
Maintenance and ongoing reliability
Door hardware is not like a light switch that you rarely touch once it works. In an active facility, door access devices see thousands of cycles. Even if your installed components are high quality, the system still depends on routine checks.
For strikes and mag locks, maintenance is typically about:
- Ensuring latch alignment and strike engagement remain correct Confirming door alignment and gap remain within acceptable tolerances Checking that door contacts and interlock sensors remain properly adjusted
If you manage multiple doors, you can also reduce surprises by keeping a record of installation settings. I have seen teams lose time because “the door stopped working” turned into a scavenger hunt for what was adjusted last and when.
Choosing an approach for your site: a decision mindset
If you are trying to decide whether your project should use electrified strikes, mag locks, or both, the best approach is to map system requirements first and pick hardware second.
Ask what you must accomplish:
- Do you need mutual exclusivity between doors? That points toward an interlock design. Do you want latch-based operation for the door? Electrified strikes support that directly. Do you need a particular mounting and surface impact approach? Mag locks can help there, but they require good alignment and power design. What do your life safety and fire alarm interfaces require during alarm and during power loss? That requirement can narrow your options significantly.
Once those answers are clear, the hardware selection becomes less of a debate and more of a buildable plan.
Where this “quick overview” leaves you next
Door interlocks, strikes, and mag locks are three pieces of the same workflow: release control, holding control, and coordinated permission across doors. The details that matter are the fail states, the accuracy of door feedback, the integration with exit and fire alarm behavior, and the commissioning tests that prove everything works under the real sequences your building uses.
If you are working on an existing site, the fastest way to get confidence is to observe one full cycle: a door unlock request, the interlock behavior, the door contact confirmation, and the system’s response when conditions change. Once you can reliably reproduce that cycle, you can troubleshoot efficiently and avoid the guesswork that costs money and disrupts tenants or operations.