Question

First, what determines the strength of an RF signal?

Why is it said that a cellphones radiates more energy when the reception from signal tower is lower in strength.
Why is it said that RF gets transmitted along wires such as in wired headsets making them act as antennae?
Is it then safer to use bluetooth headsets over wired headsets or direct usage?

Note: Do excuse if this is not purely in the realm of physics.

Answer 1

Phone's radio stack is programmed to both conserve battery and maintain the connection with base station as long as possible. So, it will increase its sending power when it receives weak signal and reduce it when the received signal is strong to save battery power.

It is just that changing EM field induces current in all conductors, so the signal from phone will induce some current in headphone cables (and vice-versa, current induced in cable by base station signal may be delivered to phone). It is not effective at all, but may help in very bad reception conditions or when phone's antenna is dumped or shielded by some material around it.
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