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Wednesday, October 6th, 2021 1:14 AM

False Alarm - Motion Sensor in Garage

We have a 2-car garage monitored by a motion sensor in one corner.
Twice in the last week, we've been woken up by a 2am alarm. The garage is accessed only by a deadbolt door, or the garage door. Both were closed each time. There are no cars in the garage, and we have no pets.
I had two thoughts, but neither seem likely.
1 - We definitely have mice here and there. Would a mouse set off a motion alarm?
2 - The door that leads to the garage has a window on the top. Would the motion sensor pick up anything through that window? (Say, someone scoping out the garage to see if anything was in it). I tested it tonight and couldn't get it to.



697 Messages

3 years ago


Long post, sorry. Summary at end if you want to skip to the meat of this post. :)

First, you should know that the SimpliSafe motion detectors are PIR (Passive InfraRed) sensors. What does this mean?

ll warm-blooded creatures (yes, even that lizard of a burglar is warm-blooded) emit infrared radiation. PIR motion sensors contain a thin film of pyroelectric material, which reacts to infrared radiation by generating electricity. A PIR Motion Sensor will trigger your burglar alarm when this influx of electricity occurs. PIR sensors are inexpensive, don't use much energy, and last forever. They're very common in indoor alarms.

Second, you should know that a window could be a problem if a headlight comes comes through and hits the sensor:

Don't point your indoor motion sensor towards a window. This is a false alarm waiting to happen -- a PIR sensor won't catch a human through glass, but it could be fooled by a car headlight or concentrated burst of sun.

Note: Light is tricky so even if the headlight isn't a straight shot to the sensor, it could reflect off of something and still hit the sensor.

Finally, there are a few other caveats that SimpliSafe lists as potential sources of false alerts:

- Direct sunlight hitting the sensor can trigger a false alarm.
- Heating vents located in the room. If they are located within the sensor's field of vision, they may cause false alarms.
- Pets that are able to get too close to the sensor. Pets under 30 pounds generally don't trigger Motion Sensors, but if they get close enough to the sensor, smaller dogs or cats may still be able to trigger it.


- Sunlight can be avoided by placing your Motion Sensor in a corner where it will not be directly hit by sunlight throughout the day.
- If you suspect that heating vents may be responsible for false alarms, position your sensor in a part of the room where it will not see the hot or cold air vent. As long as the change in the room's ambient temperature is gradual, the sensor should not trigger.

So would a mouse trigger the alarm? From afar, probably not. If it could somehow get up close to the motion sensor? Maybe.

My personal experience is that the motion detector in my garage does not pick up insects but the SimpliCam and WyzeCam in my garage definitely alert sometimes on moths and spiders and stuff. (I also have a creepy as hell video of a wood roach or something crawling across the video doorbell, pausing for a few seconds, then wandering off. :) ) That said, if something went right in front of the detector or landed on it, who knows what will happen.

In my personal experience across multiple systems (ADT (multiple generations of product), Frontpoint, SimpliSafe, etc.) the motion and glassbreak sensors are the most "finnicky" in any system. They work but they also generate the most false alarms versus an entry sensor. I'm not suggesting you don't use motion or glassbreak sensors (I have both) but wanted to give some additional feedback.

Finally, here are some other resources to look at:




In summation:

- Make sure the sensor can't catch a headlight coming in (directly or reflected off of something in the garage) through the window you mentioned
- Is there anything in the garage that might generate heat quickly? It doesn't have to be an open flame or anything but any electronics that might be kicking in and generating heat? Any HVAC stuff?
- Is the sensor somewhere that a mouse could walk right in front of it like on a shelf? If so, you may want to move it.

Good luck!



5.9K Messages

3 years ago

@jkiser I am a SS customer 9+ years and ADT before then.  Here 's the thing on motion sensors: close enough, almost anything can set them off. Spiders, mice etc. I have a motion sensor in my garage but is configured for "secret alert only". I suggest you put entry sensors on your door to the garage, and garage door(s).  I have entry sensors on both of my garage doors, taking advantage of a Youtube video where a guy used door hindges. Works great and when in home mode, the sensors are set to instant trigger. When in home mode, we are upstairs in bed and expect no one in our garage.

38 Messages

3 years ago

I have had bugs set off the motion detector on my Ring doorbell and a Z-Wave motion detector on my shed. If they get close enough, they will set it off.



113 Messages

3 years ago

Over the many years I've owned the Gen2 system, we have had 3 false alarms from motion sensors and 2 of those I could not explain.  What I ended up doing was replacing the battery.  The batteries were old and I was NOT getting a low battery notification, but there was nothing else to explain it.  I have an independent camera in the same room as one of the sensors and there was nothing that could have set it off.  The 2 I can't explain both happened in the early morning hours, like yours.  Have you ever noticed how smoke detectors tend to start beeping in the middle of the night when the battery needs to be replaced?  I think it's a similar effect on the motion sensors, and this causes some internal issue resulting in a false alarm.
If the sensors have been working fine, this is a recent issue and the batteries are old then try replacing them.



697 Messages

3 years ago


I have had bugs set off the motion detector on my Ring doorbell

FYI, Ring devices use PIR sensors but also camera/image based motion detection so they're not the same as the SimpliSafe motion detectors which only use PIR. It's possible that cameras are sometimes alerting on insects due to the camera/image detection and not the PIR.

1 Message

5 months ago

Two questions:

1 Will shadows and tree branches moving in the wind set off my Gen 2 motion sensor?

2 Can I attach a blinder on the sensor to limit its field of view?

Community Admin


2.8K Messages

@mikehamrock​ The Motion Sensor uses passive infrared to detect sources of heat moving across its field of view; things like shadows that don't emit heat should not trigger the Motion Sensor.

Placing a blinder on the sensor could prevent it from detecting motion in the areas you may want covered. We recommend placing the Motion Sensor in a corner to have an uninterrupted field of view, but in your case it could help to place it on a flat wall or a shelf.

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