If you visit any firm selling security equipment, they will be able to 
sell you 'Glass Break Detector' for attaching to a windows. They are about 
3/4" dia and contain a piezo disk ready mounted with a 2 yard cable to attach 
to windows. A bit of Blu-Tak or plasticene wil make an effective temporary 
mount. They are very sensitive and the probably the best cheap device 
available. You then need a audio amplifier (portable radio?) and some readout 
equipment, like a DVM. 
 Chris

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