why when the police are trying to ketch somebody do they put sirens on, im sure that would alert them the police are on the run, giving them the chance to find somewhere to go. If the sirens werent on they wouldn't know they were going to be captured
I have never understood this either.If the Police are going to (say) a road traffic accident etc,thats fine;but going to somewhere where the criminals may still be,its daft!
I think they're asking people to get out of the way! It's also a warning that they might be about to go through a red light. I don't think it's so easy to creep silently and quickly through jam packed traffic!!! Hence the blues and twos. :-)
Sirens usually go on when the driver in question has spotted the police, and started to make a run for it. the siren warns the driver to stop, and also warns everyone else that a chase is on.
They don't put the sirens on when they want to catch someone. They put the sirens on when they want the traffic to get out of the way so that they can get quickly to the place where the baddie is. When they get there (or if they are nearby in the first place) they put the sirens off (or don't put them on in the first place).
The cops are instructed how to approach a stop by dispatch, i.e. Code 2 is a silent alarm, use no lights or sirens. I'm sure the terminology is different in the UK, but the intent is the same. As a rule, the sirens are used to help the police get through traffic and to warn cars at intersections of their approach.