Short answer
The panel shows the zone number or name of the sensor with the low battery. Pop its cover, read the battery type off the old cell (usually a lithium CR123A, CR2032, or CR2450), replace it the right way up, close the cover firmly, and trigger the sensor once so it reports in. The warning clears on its own or when you next disarm or acknowledge it.
On this page
Find the sensor
- Honeywell VISTA: the keypad shows BAT with a zone number. BAT with no number is the panel's own battery.
- DSC PowerSeries: press * 2, then 7 to see the zones with low batteries. See DSC trouble codes.
- Touchscreen panels and app-based systems (2GIG, Qolsys, Lyric, Ring, SimpliSafe and similar): the alert names the sensor. The app usually shows it too.
If you only have a zone number, check the zone list your installer left (often a sticker inside the panel door) or walk around opening covers until you find the one with that number written inside.
Common battery types
| Battery | Typical devices |
|---|---|
| CR123A (3 V lithium) | Motion detectors, larger door/window contacts, glass-break detectors |
| CR2032 (3 V coin cell) | Slim door/window contacts, key fobs, panic buttons |
| CR2450 (3 V coin cell) | Some newer slim sensors |
| AA or AAA lithium | Some motion detectors, keypads, and sirens |
Always copy the old battery's exact type. Use lithium where the original was lithium; alkaline AAs may fit but often do not last and can trigger early low-battery warnings.
Change the battery
- Put the system in disarmed mode. If the sensor is on a 24-hour or fire zone, call the monitoring company first, because opening the cover can send a tamper signal.
- Open the cover. Most have a small slot for a flat screwdriver or a coin.
- Note the + side, swap the battery, and check the contacts are clean.
- Snap the cover shut until it clicks. A loose cover leaves the tamper switch open and causes a new trouble.
- Trigger the sensor: open and close the door, or walk in front of the motion detector.
The warning will not go away
- Give it time. Some panels only clear a low battery after the sensor's next routine check-in, which can take up to an hour.
- On Honeywell VISTA, enter your code and press OFF twice to clear the display.
- Check the new battery is fresh. Cheap or old-stock lithium cells can already be weak.
- If the same sensor drains batteries in weeks, it may be failing or sitting at the edge of radio range. That needs a technician or a replacement sensor.
Replace them all at once?
If several sensors were installed together, they tend to go low within months of each other. Replacing every battery in one visit saves repeated trouble beeps, especially overnight.