Anti-Lost alarm circuit. Help!

Thread Starter


Joined Jan 24, 2010
Hello Everyone,

Im currently working on a project and need some help starting up. I want to design an anti-lost alarm/pager circuit composed of a transmitter and receiver. When the receiver is seperated from the transmitter at 7 feet it should sound off an alarm. It needs to use RF and needs to be small as possible. I want the transmitter to run off 5v supply and the receiver can run off any voltage.

I dont know where to begin. What type of transmitter should I use? What type of parts will I need to accomplish this?


Joined Jan 28, 2005
Take a look at the website. They have a number of RF solutions that might fit your need.

As for the 7 foot range distance, That may be a toughy. You may need to use a very poor antenna since most of the RF modules go over hundreds of feet.

And then there is RFID technology that fits more into your distance criteria.



Joined Jul 22, 2007
To take some fun out of building yourself... There are commercial products, that do the very same thing. It's for keeping track of kids, although I think a collar and chain would be more appropriate in most cases.

and several others... Not suggesting you buy any of these (over priced?), but might give you something to search for more intimate details on.