LiftMaster 841LM Automatic Garage Door Lock
The LiftMaster 841LM is an automatic garage door deadbolt lock that works with select LiftMaster openers designed to control an automatic lock. When the opener closes the door, the lock extends into the track area to add a physical security point. When the opener is activated, the lock retracts before the door moves.
This lock is commonly used on lock-capable residential openers and wall-mount systems where extra garage security is desired. It can also be replaced if the original lock is physically damaged, sticking, missing, or no longer responding to the opener. Correct voltage and opener compatibility are critical because LiftMaster has used different automatic lock designs across model generations.
The 841LM is a 12V lock for select newer lock-capable models. It is not interchangeable with older 24V lock assemblies used on some previous jackshaft opener platforms. If the lock chatters, fails to retract, or creates opener errors, the lock, wiring, door track alignment, and opener output should all be checked.
Compatible With
- LiftMaster WLED
- LiftMaster 8550WLB
- LiftMaster 8360WLB
- LiftMaster 8580WLB
- LiftMaster 8587WL
- LiftMaster 8550WL and 8587WL style lock-capable systems when specified
- LiftMaster 8500W applications where the automatic lock is included or supported
- Other select LiftMaster garage door openers bearing the Security Shield/lock-ready feature when the manual calls for 841LM
Features and Specifications
| Manufacturer | LiftMaster |
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| Product Type | Automatic garage door deadbolt lock |
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| Part Number | 841LM |
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| Application | Automatic physical garage door locking |
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| Compatible Operator Type | Select LiftMaster lock-capable residential garage door openers |
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| Voltage | 12V lock system |
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| Security Technology | Security Shield / lock-capable opener systems |
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| Notes | Not interchangeable with older 24V automatic locks |
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Also Known As / Related Part Numbers
- 841LM
- LM-841LM
- Automatic Garage Door Lock
- Garage door deadbolt lock
- 12V automatic lock
- Security Shield lock
Technician Note
If the lock does not retract, do not force the door. Check track alignment, lock mounting, cable connection, opener error codes, and whether the opener is actually a 12V lock-capable model.
Before Ordering
- Confirm the opener model is listed as compatible with 841LM.
- Confirm the system uses the 12V lock, not an older 24V lock.
- Check the opener manual for automatic lock terminal and mounting instructions.
- Inspect the track where the deadbolt engages for damage or misalignment.
- Confirm whether the installation needs one lock or a lock on each side of the door.
Important Ordering Warnings
- Not interchangeable with the 24V automatic lock used on older 3800, 3900, and 8500 jackshaft opener models.
- Do not operate the door if the lock is stuck in the locked position.
- A lock error can be caused by wiring, track alignment, or opener control problems, not only by the lock.
Professional Advisory
Automatic lock service should be performed with the door stable and the opener powered down as appropriate. If the lock is jammed or the door is under tension, contact a qualified garage door technician.
Product Questions and Answers
Which openers are listed for the 841LM?
LiftMaster lists models such as WLED, 8550WLB, 8360WLB, 8580WLB, and 8587WL, and notes that the automatic lock is included with 8500W.
Is the 841LM a 12V or 24V lock?
The 841LM is a 12V lock. It is not the same as the older 24V lock used on some earlier jackshaft opener models.
Can I use this on a LiftMaster 8500?
Do not assume so. The older 8500 used a different 24V lock style, while 8500W is associated with the 841LM lock system.
What happens if the lock does not unlock?
Stop using the opener and check the lock, wiring, track alignment, and opener output. Forcing the door can damage the operator or door.
Can more than one lock be used?
Some installations use a lock on each side of the door for added resistance. Confirm the opener manual and wiring requirements before adding a second lock.
