Hi, I know very little about electronics, I'm a computer science MSc, here's what I'm after, I want to build a pair of devices as small as possible but need not be super tiny (2x4x1 cm is fine), it is a transmitter / receiver pair, they should respond to each other (one way only is needed) within the house, so, I'd say about 20 meters should be enough, but, direct line contact is not guaranteed, (rule out Infra red if I understand some of what I'm read from browsing the web), basically it should be something like your vehicle remote thing that unlocks the doors (functionality wise), just that the received part should also be as small as possible. I've read allot in the web but can't seem to understand what exactly I need, is it RF tx/rx? how much MHz is needed? is it FM? AM? I've tried but there is too much not explained in those sites, I thought someone here can help. any comment <--- appreciated bests. -tzurs.