First, I know nothing at all about this topic, which is why I'm looking for help. I'm interested in building a radio transmitter/receiver like a child locator at home. The difference would be I'd like the receiver to beep rather than the transmitter, if that's even the correct language to use. For example, if your kid (or cell phone, briefcase, etc.) strays too far, your transmitter automatically beeps and/or vibrates at a certain distance. I'm trying to find out the following questions: 2. How to have the receiver both vibrate and beep. 3. Would it be possible to have the transmitter be adjustable to various distances. 4. How small could the receiver be? 5. How much it would cost to build this at home, using the smallest units for each .Essentially I'd like the receiver to be able to fit on the back of a phone, key ring, etc., and the transmitter to be similar in size. I understand this is a lot of information, so any help is greatly appreciated, I'm at square one right now. Thanks in advance.