the police also used to deploy alarms that fed straight into their radio systems.
...
nothing was ever reference by the control room to direct officers but all other jobs were dropped very quickly.
In a related vein I recall a school teacher who had been a Met Officer in a past life telling us of a weekend when he'd come across a fight that had spilled out of a pub and seemed to be growing as rival football fans from an opposing pub joined in. A bystander suggested that he should do something about it, but being on a lone foot patrol he wasn't about to wade into a mini-riot on his own. He tried to call it in, but on his older radio the control centre couldn't make him out over the background noise.
So he pushed the Code 10 button. Code 10 was the panic button for "Officer down" and also engaged a locator signal to the control centre.
Apparently within 4-5 minutes he had four panda cars, two district support units (~16 burly riot-clad officers), a couple of armed units, some traffic cops and a dog unit along with the obligatory ambulance all asking where the downed officer was.
He was asked not to do that again unless it was actually a code 10.
The sudden, noisy appearance of most of West London's on-duty Police apparently broke up the mini-riot without requiring any direct intervention.