Burglar alarm systems serve two basic purposes: alerting those both inside and out of a property to the presence of an intruder and deterring potential criminals from entering a property in the first place. When an alarm goes off, it should, in theory, stop a burglar in their tracks, or at least raise awareness of the crime to passers-by; someone may look out of their window and see an unfamiliar figure approaching the property across the street, therefore being able to act as a witness if the authorities become involved.
Though some burglar alarms are successfully triggered by the unexpected motion caused by break-ins, studies have shown that an audible alarm may not always have the intended effect. In a 2012 survey, 87% of those questioned said they would ignore a neighbour’s burglar alarm if they heard it going off. This phenomenon has been dubbed “alarm fatigue”, alluding to the fact that people are tired of hearing alarms because they hear so many as to not take them seriously.