Intruder Alarms Flashcards
In a normal closed alarm circuit state why windows may be opened when panel is not activated
They are shunted by diodes
Current passes through the diodes
In a normal closed circuit state why the system is activate when a window is opened on an armed alarm system
Polarity reverse
Diodes block current so Current flows through alarm contacts
When a window is opened flow of current stops
What is a panic button
Closed contacts
When button is pressed a signal is sent to the alarm panel sounding the alarm
Works if system is set or unset
Exit/entry or bedroom
What is a inertia sensor
Gold plated ball in a pair of contacts
If sensor is vibrated the ball will be unseated opening the circuit
Located on Windows
Disadvantage of closed loop circuit
Can be shorted out by an intruder with no indication given
Can be fixed with an end of line resistor
Advantage of a closed loop circuit
If a cable is cut the alarm will sound
Operation of a closed loop circuit
Alarm is activated when normal closed contact opens
De-energises the alarm relay
Resistance on open circuit
Infinity
Resistance on short circuit
0
Max bell box sounding time
15 mins
Min bell box noise level
70db
Different types of intruder detectors
PIR
Magnetic reed switch
Pressure mat
Infrared beams
Inertia sensor
Tamper circuit
Interfere with the system triggering anti tamper device, alarm will sound if system is armed or not
Magnetic reed switch location
Doors
PIR Location
Hallway or upstairs landing
