Help building an alarm system....?

Have trawled the internet looking for the diagram I need but had no luck (perhaps I'm typing in the wrong things to search for)..... I basically need to build an alarm system comprising of a siren which is triggered by one wire when it is cut. So imagine if you can the siren and a wire running out of one side, in a big circle and then going back into the siren, and if this wire is cut/broken the alarm sounds.