Normally closed to normally open alarm circuit

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peters.carl

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I have a 12v power supply and a flow switch which is closed when water is flowing through it and open when water isnt. I want to make a simple piezo alarm + LED light that tells me (comes on) when water STOPS flowing. How do I do this? That is, how do I take a normally closed switch and make it normally open? Simple is best for me and the less power consumption the better.

Many thanks.
 

This looks perfect. can you point me to the correct npn transistor on rs electronics website? (excuse my ignorance) thanks heaps
 

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