The number of devices doesn't really matter, but it does influence something like a duty cycle. It's all about power level, distance, and duty cycle. Sure, the

The number of devices doesn't really matter, but it does influence something like a duty cycle. It's all about power level, distance, and duty cycle. Sure, the cell phone antenna is going to transmit at something like 1kW, but its also significantly further away from you. Inverse-square law is a hell of a thing, so something being really close to you will end up imparting more effective energy than something far away.