Forgive me if you know this Eglantine but there are different types of burglar alarms, so do not be under the illusion that the police will necessarily hot foot it round to your house if one goes off. A basic bell alarm merely rings audibly if tripped, and that is all. Will depend on neighbours or those nearby to investigate. Some will be connect automatically to your smart phone or designated numbers to let you know it has gone off. Some are monitored by a company, for an annual fee, and they will inform you, or designated key holder when the alarm goes off. Some require a much larger annual fee and are monitored and the company will also contact the police when your alarm triggers. There's no guarantee of a rapid response by the police even for this type of alarm because they will prioritise according to availability of resources.