I want to make a mobile call/sms detector

[hrshovon]

I have always been noticing one thing that whenever I put my mobile near my pc speaker....when the phone rings(incoming calls actually),speakers generate noise.That means these pc speakers detects the frequencies and return an oscillating voltage...I tried to detect incoming call with a wire that i put on my mobile but i found nothing detectable in my multimeter(neither ac nor dc).I built a transistor based amp but it didnt return anything hopeful.then i built a non inverting amp but that also failed...now i want to know why my speaker is detecting that and my long wire is not.Thnx for reading my post.

[george.brooks]

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