"Andrew Gabriel" wrote in message
...
In article ,
Alan writes:
In message , "dennis@home"
wrote

the theory was that you wanted to catch burglars in the property not
scare them away.

Isn't the aim to deter burglars from a domestic property hence the
prominently displayed external bell box.

Yes - that's the first aim.
Burglar alarms don't 'catch' burglars. Police used to temporarily
supply silent alert systems where they wanted to catch someone, but
if you aren't the police, you don't want to encounter a burglar,
you just want them to scarper empty handed as fast as possible.

I think the real reason it was done the way it was was because if you alarm
a locked door (i.e. the periphery) the alarm will never go off because the
bugler will find a weaker spot. The sensors were always fitted to internal
doors that were likely to be used by a burglar.

Now PIRs are so cheap you don't need to protect the periphery at all.