thanks for your input guys. I havent been able to come online due to power outages caused by hurricane wilma.

anyway. the reed switch mentioned would work, but the distance is the issue. I currently have an rfid reader and passive tag, but they too work only within a few inches. What I need is for the device to be activated within 5 feet of the receiver and from my understanding a reed switch cant do that.

I know electronic toll payment systems seem to conserve battery, and thats what i need. Bascially I want to have a battery in the unit, but I dont want the battery to be connected until we're in that range. The reason passive devices dont work is because even though the antenna can provide an induced current, without a battery the tag doesnt have enough power to be able to transmit over say a few inches, let alone five feet. So we need battery in the transmitter. The user only carries a transmitter, so it doenst know when it is within range. I have a microcontroller that will transmit an ID as soon as it is powered up, but I dont want it to be on at all times, and I dont want a switch. I'll look into the "Hall Effect" now and see what its about.

Thanks again guys, keep it coming.