In every intercom or video doorbell project there is a moment when someone asks how the door actually opens. The screen, the camera, the call routing — all of that gets specified carefully. The unlock path is often a one-line note: "with electric lock". That one line hides more project risk than anything else in the bill of materials.
Unlock is a relay output, not a feature
The panel does not energize a lock. It closes a relay — a switch — for a set duration. Everything else belongs to someone else: the lock's power supply, the wiring, the lock's own behavior. This is why the output's specification matters more than its existence. Is it a dry contact with no voltage of its own, or does it carry power? Normally open or normally closed? What current can it switch, and for how many seconds?
A dry contact rated for low current, connected to a lock that draws more, will behave perfectly in the demo and weld itself shut in month eight.
Two lock families with opposite failure modes
Electric strikes — the latch in the door frame — are usually fail-secure: no power, door stays locked, entry only from inside. Electromagnetic locks are fail-safe: no power, the door opens. One protects property during a power cut; the other protects escape routes during a fire. Building codes decide which doors may use which, and the answer differs between a home's front door and an apartment building's stairwell door.
Choosing the wrong family is not an inconvenience; it is a compliance problem discovered at inspection. The two families also need opposite relay logic — one releases on a pulse, the other on loss of power — so the panel's output mode must match the lock, not the other way around.
Who powers the lock is a real question
The lock needs power, and it can come from the panel's own auxiliary output or from a separate supply at the door. Panel-powered keeps the bill of materials short but pushes current through the same run that already carries video and audio — on long or thin cable, voltage drop at the lock becomes real, and strikes that receive marginal voltage behave erratically long before they fail outright.
A separate lock supply, with the panel's relay merely switching the circuit, is the more robust pattern. It also isolates lock faults from panel faults, so a failed strike does not take the intercom down with it.
Duration, re-locking and human habits
Unlock duration is a human-factors setting. Too short and visitors fumble the heavy door; too long and the access control is mostly decorative. Three to five seconds is typical, with re-locking that should be decisive — the latch should not hang half-open for the next visitor to wander through. Requests-to-exit from the inside, a button that releases the lock, belong in the same design; otherwise the first fire drill reveals that people exit through a door the system never considered.
One bus, many doors
Multi-tenant systems multiply all of this. The unlock signal must travel the riser to the right door, and each door may have a different lock type. Panels that expose per-door relay outputs over the bus make this clean; panels with a single shared output force compromises that show up as doors unlocking in groups — an acceptable bug in a villa, an audit finding in an apartment building.
Specify it in the RFQ, not on site
Five lines that belong in the request for quotation: output type and contact rating; supported lock types, fail-safe and fail-secure both named; power source for the lock and expected voltage at the lock after cable drop; unlock duration range; and fire-code compliance for the door in question. Doorbell and intercom panels in our video doorbell category carry these outputs as first-class requirements — as a video intercom manufacturer we would rather answer lock questions at quotation than at commissioning. Factory background: xingliaotech.com; project inquiries: contact.
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