[Sensor alarm and transmitter]

Link below to circuits of what I'm looking for but in reverse.  don't need all the extras this comes with but just a detector and some kind of transmitter

http://www.google.com/patents/US5652569

 

[Sensor alarm and transmitter]

Hiya, I now cant find the projects I found yesterday sorry... but the below link is a device similar to what I'm looking for, but I'm looking to make this work in reverse (hoping this may help).  The distance I'm trying to achieve would be for the alarm to activate if transmitter was anything from 0-10 feet away.

http://www.pimall.com/nais/rdiftagalert.html

[Sensor alarm and transmitter]

Hey guys,

I'm trying to make a proximity alarm and having trouble finding info.  I can find plenty of examples for projects for an alarm and transmitter where as soon as the transmitter is a certain distance away the alarm flashes.  What I'm wanting is the opposite,  as soon as the transmitter is within a certain distance the alarm flashes.  I'm sure this is as simple but I'm completely new to electronics so have no idea if its as simple as reversing a few things etc???  I don't even know the correct name for this product??  Any help or direction on this subject would be greatly appreciated.

Cheers