LiftMaster 841LM Automatic Garage Door Lock
Automatic track-mounted deadbolt designed to add another layer of security to compatible LiftMaster residential garage door openers.
The LiftMaster 841LM Automatic Garage Door Lock secures a compatible sectional garage door by automatically extending a steel locking bolt through the vertical track after the door reaches the fully closed position.
Before the opener raises the door, the lock automatically retracts to release the track. This coordinated operation helps prevent the door from being manually forced upward while eliminating the need to remember to engage or release a separate manual slide lock.
Automatic Deadbolt Security Extends a steel locking bolt through the garage door track whenever the compatible opener closes the door.
Opener-Controlled Operation Automatically retracts before the opener begins lifting the garage door.
Track-Mounted Design Mounts directly to a compatible vertical garage door track near one of the door rollers.
Key Features
- Automatic garage door track lock
- Steel deadbolt extends through the vertical track
- Engages automatically whenever the door fully closes
- Retracts automatically before the opener raises the door
- Helps prevent the closed garage door from being manually forced upward
- Eliminates the need to operate a separate manual slide lock
- Hardwired communication with the compatible garage door opener
- Designed for select LiftMaster lock-capable residential openers
- Replacement lock includes an extended connection-wire length
- Genuine LiftMaster residential security accessory
Product Specifications
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Manufacturer: LiftMaster
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Model Number: 841LM
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Product Type: Automatic garage door track lock
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Locking Method: Automatic steel deadbolt
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Operating Voltage: 12V
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Connection Type: Wired connection to compatible opener
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Mounting Location: Garage door vertical track
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Door Application: Compatible residential sectional garage doors
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Replacement Wire Length: Approximately 33.5'
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Package Quantity: One automatic garage door lock kit
Compatible LiftMaster Openers
- WLED
- 8550WLB and compatible 8550WL-series models
- 8360WLB and compatible 8360WL-series models
- 8580WLB
- 8587WL
- 8500W lock-capable wall-mount opener systems
Compatibility can vary by opener production date and exact model suffix. Always verify the opener model number and confirm that it has the designated automatic-lock connection before ordering.
12V Lock Compatibility: The 841LM is a 12V automatic lock and is only compatible with designated 12V lock-capable opener systems. It is not interchangeable with the 24V power lock used on older LiftMaster 3800, 3900, or original 8500 residential jackshaft openers.
How the Automatic Lock Works ```
- The compatible garage door opener lowers the door to the fully closed position.
- The opener sends power to the automatic lock.
- The steel deadbolt extends through a prepared opening in the vertical track.
- When the door is activated, the lock retracts before the opener begins lifting.
- The opener then raises the unlocked garage door normally.
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Track Preparation Required: Installation may require drilling a 3/4-inch deadbolt opening and two 5/16-inch mounting holes in the vertical track. The lock must be positioned above a door roller and aligned so the deadbolt moves freely without contacting the roller, track edge, or door hardware.
Battery-Backup Operation: On compatible DC openers equipped with battery backup, the lock may disengage once during a power outage to allow garage access. It will not automatically engage again until normal electrical power has been restored.
Not a Wind-Load Center-Post Replacement: If the garage door requires a removable center post, reinforcement system, or other hardware during a high-wind event, the 841LM cannot be used as a replacement for that required system. Wind-load compliance must follow the garage door manufacturer’s specifications and applicable building codes.
Compatibility Notice
Verify the exact garage door opener model, operating voltage, automatic-lock connection, vertical-track style, roller position, available mounting clearance, wiring route, battery-backup configuration, and door construction before ordering. The presence of myQ or Wi-Fi alone does not confirm compatibility.
Additional Lock Option: Some compatible LiftMaster opener models can support up to two automatic garage door locks, allowing one lock to be installed on each side of the door. Confirm the opener’s specifications and connection requirements before adding a second lock.
Safety Warning: Disconnect electrical power and battery backup before installing or servicing the lock. Secure the garage door in the fully closed position, keep hands clear of the deadbolt and track openings, and manually test that the lock fully retracts before operating the opener. Installation should be completed by a qualified garage door professional when track modification or opener compatibility is uncertain.
