Common Causes of False Alarms
1. User Error
User error is the biggest cause of false alarms. It is critical for the alarm installer to train their customer on how to operate the system and follow procedure such as closing windows and doors, securing the family pet and following the correct entry/exit route.
2. Checking the AC/DC supply
When a false alarm occurs which hasn’t been triggered by user error, the first thing that should be checked is the AC/DC power supply. It is critical for the AC/DC supply to be stable to prevent random false alarms and control panel crashes. An AC supply fault or low capacity battery would cause PIRs to trigger falsely and cause LIMs to lockout.
Alarm installers have a duty of care to ensure the AC supply is safe BEFORE connecting the control equipment. Voltage, polarity and Earth loop resistance are the most essential safety tests to perform when checking this power supply. Loop faults can only be performed using a mains multitester such as the ACT Easiplus. Test for stable DC voltage between 13.5 min and 14.0 max at battery, PIRs, keypads and LIMs. Remember, AC/DC problems can only be prevented by testing during installation and service inspections.
3. Interference
If an unstable AC/DC power supply is not the cause of the false alarm, the next likely cause is electrical interference.
Radio Frequency Interference (RFI), Electromagnet Interference (EMI) and Electro Static Discharge (ESD) can cause big problems for alarm and other electrical systems.
RFI - caused from signals omitted by an external source such as the local police office, taxi CB or HAM radio equipment – will cause specific PIR or shock sensors to activate.
EMI - caused by AC voltage induced from electrical wiring or kitchen appliances into DC alarm cables - will cause random PIR or shock sensors to activate or the control equipment to crash.
ESD - caused by seasonal weather changes and lightning – will cause keypads to lock out or the control panel to crash when the user enters their entry/exit code.
The Solution
Random false alarms and panel crashes can be prevented on new installations and troubleshooting inspections by fitting an ACT 2323 mainspike suppressor and ACT 1313 12V spike suppressor as standard. Unexplained false alarms on specific alarm detectors can be prevented by fitting an ACT 1376 PIR stabiliser inside the troublesome PIR or ACT 3010 ferrite tubes over the DC wires inside the troublesome shock sensor.
Identifying False Alarms by RFI
Visual Inspection
Go outside and look for close sources of RFI signals, CB/Ham radio aerials, local taxi ranks and police, fire and ambulance stations.
Mobile Phone
Place the aerial of your mobile phone against the PIR cover and standing perfectly still so you don’t activate it, dial a number and press send. This test can be performed on any power detector.
Cover
Mask the troublesome PIR securely with a business card or PVC tape and put the circuit on a soak-test
Finally
If RFI is identified as a potential cause of fire alarms, don’t fit a dual microwave/PIR. Microwave is a receiver of RFI and could give more false alarms than an ordinary PIR
Four Steps to Eliminate RFI
1. Instead of changing the detector with an identical PIR, go through our ‘PIR fault finding checklist’ to prove the cause is RFI
2. Swap the troublesome PIR with another in the same building
3. Fit an ACT 1376 PIR stabiliser inside the troublesome zone PIR and put the circuit on a soak-test
4. If a false alarm moves to the other zone, change the PIR and recover the PIR
Five Causes of PIR False Alarms
1. The first cause of PIR false alarms is low or unstable voltage at the detector. Test to make sure the voltage at each PIR is above 13VDC and stable.
2. The second cause of false alarms is sudden infrared movement / heat changes in view of the detector. Check behind and inside the PIR for insects and identify objects that can move or rapidly change temperature (e.g. pets, vermin, fax, mailbox, radiator or boiler etc).
3. The third cause of false alarms is white light momentarily blinding the detector. Always choose PIR’s with genuine white light filters and avoid fitting facing glass with 50% of its operating range.
4. The fourth cause of false alarms is a direct draught striking the detector. This causes air convection inside the PIR. Make sure cable and screw holes are totally sealed and don’t forget the hole where the cable comes through the cavity wall or ceiling.
5. The fifth cause of false alarms is RFI/EMI signals. A mobile phone can be used to test susceptability to RFI by placing the aerial against the PIR casing and transmitting. Fit an ACT 1376 stabiliser inside the PIR to eliminate RFI.
