What kind of transmitter and receiver should i use?

Hey all, i hope someone out here can give me some guidance. I am trying to come out with a circuit to detect the distance between a device holder and the device. I want to use a transmitter and receiver circuit with arduino and a LED. What transmitter and receiver do you suggest? It should be able to detect up to 3m and when the device is outside the 3m range the LED will start blinking.

Simple transmitters/receivers usually don't reliably detect distance, if that is what you are wanting.

Ya i got that point because i am having a hard time figuring out which transmitter and receiver i am suppose to use to make that work. I just want to know which transmitter and receiver can make this work.

I just want to know which transmitter and receiver can make this work.

No transmitter / receiver can make this work, it is a flawed idea.

In principle you could have the device transmit radio signals or generate an alternating magnetic field, and have the device holder measure the received intensity. The problem with implementing this is that it is impossible to have a transmitted field that is uniform in all directions. I think you would need at least 2 transmitters and 4 receivers to make this idea work.

Another possibility would be to have the device holder transmit ultrasonic pulses, and have the device receive them and transmit pulses back, preferably at a different frequency (like an aircraft DME system in reverse). The device holder can measure the interval between transmitted and received pulses.