I want to make a very power conservative product, and attempt to have the battery last days, or maybe even weeks. This device would consist of 2 modes, a mode which would have more functions but use bluetooth and more battery, and a mode ( this one is the one I'm asking about) which would only "complete" it's circuit, or use power, when receiving a signal from my phone, I was wondering if there's any way I could use a similar concept of RFID tags absorbing the energy from the radio waves themselves, to complete my circuit? The product will have it's own battery but the idea is to make the battery last as long as humanly possible in this mode. This whole idea is supposed to be as small as possible so let's say it's 2D dimensions would be at max the size of a penny ( So I can't have some big intricate system). Any ideas?

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