Sensing device plz help

First of all im not sure if this is the correct topic, sorry if im wrong.
What i want to make here is a device that can emit sound when a tag is within the device range.
For example, the sound emitting device is placed on a table and a person carry a tag on him. When the person is near to that table, the device will emit sound.
I need some guide on how to achieve this. Like what component should i use?
Thanks for the reply

Google RFID systems

Dave

RFID would work, specially if the "tag" has to be passive (no power supply), but you have to orient it correctly with respect to the reader. A quick solution with prototyping boards, would be to have an RF transmitter (cheap 430 MHz) be the "tag" transmitting some code, and the device on the table be a receiver. As soon as it can read whatever the tag is sending (known before hand), it makes a sound (piezo buzzer). If you can make the receiver/transmitter yourself, you would transmit a tone and detect power.

JP