A burglar alarm is an object that can be bought in buy mode to automatically alert the police that a burglar is on the property.
Tips
In all games, it is impossible to enter Build Mode or Buy Mode after a burglar enters the lot. It is important that players properly secure the lot before a burglar arrives.
In The Sims, an easy way to make a house burglar-proof is to build a single wall on both sides of the lot and put a burglar alarm on each; when a burglar enters the lot, the alarms will be set off instantly, resulting in the police being summoned immediately; often before the burglar can even enter the house.
In The Sims 2, burglar alarms cannot be placed outside (except by using the move_objects cheat or by tricking the game), so each room with a door to the outside should have an alarm.