An audible or visual deterrent may be effective in
disrupting the intruder but is unlikely to summon assistance
from the police. Under the current ACPO security systems
policy most Police forces will not respond to an unmonitored
alarm system unless there is first hand evidence that an
offence is in progress.
A monitored alarm system using a digital communicator,

or
DualCom is connected 24 hours
a day to an Alarm Receiving Centre manned by professional
operators. On receipt of an alarm signal a key holder is
contacted and the appropriate action taken by the operator to
confirm the Alarm is genuine and the Police or Fire services
notified.