How to Replace the Battery in a Wireless Motion Detector
When a motion detector stops reporting or flags a low battery, it is almost always the battery -- not the sensor. Here is how to swap it on a 2GIG PIR1 motion detector and confirm the room is still covered.
The 2GIG-PIR1-345 passive infrared motion detector is a common wireless sensor we install, and it runs on a single CR123A lithium battery. When you get a low-battery or tamper alert, put the system in test mode, remove the screw at the bottom of the case, lift the main body off the wall-mounted back plate, and swap in one fresh CR123A observing the marked polarity. Press the tamper to power it back up, then walk-test it to confirm it still covers the room.
Key Takeaways
- 1A low-battery alert points to the battery inside the detector, not a fault with the sensor itself
- 2The 2GIG PIR1 uses one CR123A lithium battery -- not a coin cell like a door/window sensor
- 3You do not remove the detector from the wall -- the back plate stays mounted and only the main body comes off
- 4Observe polarity when seating the CR123A, and leave the pet-immunity and sensitivity jumpers exactly where they are
- 5After the swap, press the tamper to power up and walk-test the detector to confirm coverage
A motion detector watches a whole room, so when one drops off or flags a low battery, that is a real gap -- an area your system is no longer covering. It is easy to assume the sensor failed. Usually it did not. The battery inside has just run down.
This guide covers the 2GIG PIR1 -- model PIR1-345 -- a passive infrared motion detector we install and service on a lot of systems. Unlike a door or window contact that uses coin cells, this one runs on a single CR123A lithium battery. The swap takes a few minutes. Here is how we do it.
What you need
One fresh CR123A lithium battery and a small screwdriver for the bottom case screw. The PIR1 takes a single Panasonic CR123A, or an equivalent lithium cell -- use only the recommended battery. Before you open anything, put your panel in Walk Test mode or disarm the system. The detector has a tamper switch, and opening it on a live system can trip the alarm or signal your monitoring center.
Step 1: Put the system in test mode
From your panel, put the system into Walk Test mode (or at minimum, disarm it). This keeps the tamper from setting off the alarm while you work, and it sets you up to walk-test the detector at the end without leaving the panel.
Step 2: Remove the bottom screw and release the case
There is a single screw at the bottom of the case that holds the main body to the back plate. Back it out. If the body does not release on its own, slide the tip of a small flathead into the bottom seam and ease it loose. Work gently -- you are just releasing the bottom edge.
Step 3: Lift the body off the back plate
With the screw out, pull the main body away from the back plate, working from the bottom up. The back plate stays screwed to the wall -- you are not taking the detector down or disturbing its aim. Only the body, with the board and battery inside, comes off.
Step 4: Swap the CR123A -- mind the polarity
Lift the old CR123A out of its holder and drop in the fresh one, matching the plus and minus marks molded into the case. Reversed polarity is the most common reason a detector will not come back up after a battery change, so take the extra second to check it. While you are in there, leave the two jumpers -- pet immunity on the left, sensitivity on the right -- exactly where they are set. Pulling them changes how the detector behaves and can cause false alarms.
This is a lithium battery. Handled improperly, it can generate heat, rupture, or catch fire, so do not recharge, disassemble, short, or dispose of it in fire. Keep new and used batteries away from small children -- if one is swallowed, see a doctor promptly. Do not throw it in the household trash; dispose of it per your local recycling regulations. California residents: this cell carries a perchlorate handling notice.
Step 5: Power it up and walk-test it
Press and release the tamper switch to start the power-up, then give it about 10 seconds. Set the main body back onto the back plate and drive the bottom screw back in. Now confirm it is working: with the panel in Walk Test mode, hold the supplied magnet over the arrow on the left side of the detector -- the LED lights to show it registered -- then take the magnet away. Move through the area the detector covers and watch the LED flash each time you move, with a few seconds between flashes. If it lights and tracks your movement, you are done. If it will not power up or report, that is the point to flag it for service rather than guessing.
Test with the cover on. Walk-testing with the body off, or with a jumper removed, can throw a false reading -- so close it up first, then walk the room.
A motion detector that drops off usually isn't broken. It's a dead CR123A -- and a room that's quietly gone uncovered until you swap it.
Your Checklist
- Confirm the battery -- the 2GIG PIR1 takes one CR123A lithium cell (Panasonic CR123A or equivalent)
- Put the panel in Walk Test mode (or disarm) before opening -- the detector has a tamper
- Remove the single bottom screw; the back plate stays on the wall and the aim stays set
- Seat the CR123A observing the polarity marked in the case
- Leave the pet-immunity and sensitivity jumpers exactly where they are
- Press and release the tamper to power up, then wait about 10 seconds
- Reattach the body, drive the bottom screw back in, and walk-test until the LED tracks your movement
Common Mistakes to Avoid
Installing the CR123A backwards
Reversed polarity is the number-one reason a detector will not come back up after a battery change. Match the plus and minus marks in the case before you close it -- a backwards cell reads exactly like a dead sensor.
Pulling or moving the jumpers
The two jumpers set pet immunity and sensitivity. Remove one and the detector can false-alarm or behave differently than it did before. Leave them exactly as you found them unless you are deliberately re-tuning coverage.
Trying to take the whole detector off the wall
You only remove the main body. The back plate is screwed to the wall and keeps the aim set. Pull the detector down and you risk changing the coverage angle you carefully set at install.
Skipping the tamper press and the walk test
The PIR needs a tamper press and about 10 seconds to power back up. And fresh battery in hand is not the same as a proven-covered room -- walk-test it in the panel test mode and confirm the LED tracks your movement.
Using a rechargeable or non-recommended battery
Use only the recommended CR123A lithium cell. Rechargeables and off-spec batteries can under-power the detector or shorten its life -- and lithium cells should never be recharged, disassembled, or burned.
Frequently Asked Questions
What battery does the 2GIG PIR1 motion detector take?
One CR123A lithium battery -- the manual specifies a Panasonic CR123A or an equivalent lithium cell. It is a common 3V camera-style battery, not a flat coin cell like a door/window sensor uses. You can find it at most hardware stores, pharmacies, and online.
Do I have to take the detector off the wall to change the battery?
No. The back plate stays screwed to the wall, which keeps the detector aimed the way it was set. You remove the single screw at the bottom of the case and lift the main body off from the bottom up. Taking the whole unit down risks changing its coverage angle.
Do I need to re-enroll the detector after changing the battery?
Usually not. Press and release the tamper switch to power it back up, wait about 10 seconds, then walk-test it. If it never reports after a fresh, correctly seated battery, it may need to be re-enrolled -- on a 2GIG panel that means putting the panel in learn mode and holding the tamper switch for about two seconds. If it still will not report, that is worth a call.
Will the alarm go off when I open the detector?
It can. The PIR1 has a tamper switch, so opening the case while the system is armed can trip an alert or signal your monitoring center. Put the panel in Walk Test mode or disarm it before you start, and you avoid setting anything off.
How do I know the detector still covers the room after the swap?
Walk-test it. With the panel in Walk Test mode and the cover back on, hold the magnet over the arrow on the left side of the detector -- the LED lights to confirm it registered -- then remove the magnet and move through the coverage area. The LED should flash each time you move, with a few seconds between flashes, for about a minute.
Are the batteries safe to handle and toss in the trash?
They are lithium cells, so handle them with care -- do not recharge, disassemble, short, or burn them, and keep new and used batteries away from small children. Do not put them in your household trash. Dispose of them according to your local recycling regulations, and note that in California these cells carry a perchlorate handling notice.
Related Services
Managing a building full of sensors and tired of chasing low-battery alerts?
With a PAXCare plan, we keep an eye on device health and handle the maintenance before a dead battery turns into a blind spot. Licensed in NY and NJ.