Your security system shows it’s armed, but the motion sensors aren’t detecting movement when they should. This creates a dangerous gap in your home protection, leaving you vulnerable despite thinking you’re secure.
Step-by-Step Fixes
Step 1: Check the System Status Panel
Start at your main control panel or smartphone app. Look for any error messages or sensor status indicators. Most modern systems from ADT, Vivint, or SimpliSafe will show a small icon next to each sensor. If you see a yellow triangle or red X next to your motion sensors, that’s your first clue something’s wrong.
Step 2: Test Each Motion Sensor Individually
Walk directly in front of each motion sensor while watching for the LED light (usually red or blue). Most sensors flash when they detect movement. If there’s no light at all, the sensor might not be getting power. Try this with each sensor in your home, making note of which ones respond and which don’t.
Step 3: Power Cycle Your Security System
Turn off your main security panel by unplugging it from the wall outlet. Wait 30 seconds, then plug it back in. This simple reset often fixes communication issues between the panel and wireless sensors. While the system reboots, you’ll hear beeps and see lights cycling through startup sequences.
Step 4: Check and Replace Sensor Batteries
Motion sensors typically use CR123A or AA batteries that last 3-5 years. Open each sensor’s cover (usually by pressing a tab or unscrewing) and check the batteries. Even if they’re not completely dead, weak batteries can cause intermittent failures. Replace them with fresh ones from brands like Duracell or Energizer.
Step 5: Clear Sensor Obstructions
Dust, spider webs, or even furniture placement can block motion sensors. Use compressed air to blow out any debris from the sensor lens. Make sure nothing like curtains, plants, or decorations are hanging in front of the sensors. These PIR (Passive Infrared) sensors need a clear view to detect body heat properly.
Step 6: Re-sync Sensors to Your System
If individual sensors still aren’t working, they might need re-pairing. Access your system’s installer menu (check your manual for the code, often something like *5555 or #9999). Select “Add Sensor” or “Learn Sensor” mode, then trigger the problematic sensor by pressing its test button. The system should beep to confirm successful pairing.
Likely Causes
Cause #1: Dead or Dying Batteries
Motion sensors drain batteries faster than door sensors because they’re constantly scanning for movement. In 2025, even with improved battery technology, cold weather or frequent triggering can shorten battery life significantly.
To check: Look for a low battery indicator on your panel or app. Some sensors also chirp or flash yellow when batteries are low.
What to do: Keep spare batteries on hand. Mark your calendar to check all sensor batteries every January and July. This routine maintenance prevents most sensor failures.
Cause #2: Wireless Interference
Your motion sensors communicate with the main panel using radio frequencies (usually 319.5 MHz or 433 MHz). Other devices like baby monitors, wireless routers, or even LED lights can interfere with these signals.
To check: Notice if sensors fail more often when certain devices are running. Problems might be worse in specific rooms or at certain times of day.
What to do: Move wireless devices at least 3 feet away from sensors. If interference persists, consider upgrading to sensors that use encrypted 2.4 GHz communication, ideal for homes with lots of smart devices.
Cause #3: Sensor Placement or Environmental Issues
Motion sensors work best when mounted 6-8 feet high in room corners. They struggle with detecting movement directly beneath them or through glass. Heat sources like vents or sunny windows can also trigger false alarms or prevent proper detection.
To check: Observe if problems occur during specific weather conditions or times of day. Test sensors by walking different paths through the room.
What to do: Relocate sensors away from heat sources and windows. Angle them to cover entry points rather than looking straight across rooms. This positioning is best used in high-traffic areas where intruders would likely walk.
When to Call Expert Help
Contact your security company’s technical support when you’ve tried all basic troubleshooting without success. Professional help is essential if your control panel shows system tamper alerts, multiple sensors fail simultaneously, or you hear unusual clicking or buzzing from the main unit.
Don’t wait if you notice burn marks, melted plastic, or smell electrical burning near any component. These signs indicate serious electrical issues not recommended for DIY repair.
Most security companies offer 24/7 support included in monitoring plans. They can run remote diagnostics and often fix software issues without sending a technician. If they do schedule a visit, they’ll arrive with replacement parts specific to your system model.
Copy-Paste Prompt for AI Help
“My home security system (brand: [YOUR BRAND]) shows it’s armed but motion sensors aren’t detecting movement. I’ve checked batteries and cleared obstructions. The main panel model is [YOUR MODEL] installed in [YEAR]. Affected sensors are in [ROOM LOCATIONS]. What specific troubleshooting steps should I try for this system? Include any button sequences or menu options I need to access.”