The number of alarm systems installed in schools mushroomed in the 1970s and 80s. But their maintenance and operation has often been inadequate. In those days there was a prevailing view that the police would always turn up, wait for the key holder to arrive, check the property and then go off about their business. Until the alarm went off again.

In the five years to 1993, faulty equipment and errors formed more than 92 per cent of all alarms. Last year the West Midlands police received more than 54,000 alarm calls: more than 47,000 of them were false - at an average cost of Pounds 120 each.

These represented a tremendous drain on police resources and led the Association of Chief Police Officers (ACPO) to draw up a national policy on response to building alarms - though there may be some local differences in interpretation.

The stated aim is to “enable the police to provide an effective response to genuine intruder alarm activations, thereby leading to the arrest of offenders and reduction of losses by improving the effectiveness of alarm systems and reducing the number of false calls.”

If you want the police to come to your school when the alarm goes off, then it must meet relevant British Standards. It must be installed and monitored by a central monitoring station that complies with police requirements. The police then issue a Unique Reference Number (URN).

If an alarm is activated, the audible and visual signs must be delayed for 10 minutes to allow the police enough time to respond. If you cannot meet that requirement, a lower level of police response may be imposed.

Bell-only alarms which do not signal to a recognised central monitoring station will not be issued a URN. Police will not normally attend to these unless other information suggests a crime is taking place; perhaps a neighbour sees something happening and dials 999.

Under the ACPO policy, the police have three levels of response: u Immediate.

u Delayed although police attendance is desirable.

u None. The key holder only will respond.

The performance of alarm systems with a URN is monitored. All will initially receive level one response but after four false alarms in any 12-month period the police response will be downgraded to level two. The school would be notified in writing of any change.

After seven false alarms in 12 months, level three is imposed and police response withdrawn.

Level one can be restored after a period free from false alarms (normally three months). In this case, the occupiers of the property would have to reapply to the police and will be expected to produce evidence that the alarm is now error-free and what corrective actions have been taken. Some police forces will make a charge to cover the administrative costs involved - from perhaps Pounds 10, plus Pounds 100 for any subsequent false alarms.

The “good old days” have gone. The police are no longer prepared continuously to attend false alarms. Tell the police if you subsequently find signs that someone did try to break in - don’t have false alarm reports wrongly attached to your system.

The police do not want to remove cover from schools; they want instead to encourage better management of alarm systems and will help headteachers towards that aim.

These policies have led to an increase in the use of verified systems which have some means of viewing, listening or otherwise confirming that the activation is good or not.

Sounds and images can be compressed and transmitted down a telephone line to the monitoring station where operators decide whether to pass on notification to the police or to the key holder alone.

John Alexander is a security adviser and director of People, Property and Security Ltd.