Are you sure the sound is continuous - sometimes what people convey in 
their description isn't what they intend to. (eg "Makes a high pitched 
noise all the time" may mean eg "... in a burst every 5 minutes 
without fail."

If it's an occasional chirp, try looking for a smoke alarm with a low 
battery. It really does happen that people fail to realise what makes 
this noise.


        Russell

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