Radio Shack sold, until recently, such a device.



kd6532 wrote:
I am designing an automated mailbox system that, after sensing an
object in the mailbox, will send an RF signal from the mailbox to a
receiver inside the home. To do so I am using a 555 timer to generate
the tone, and on the receiving end, I am using a LM567 tone detector to
detect this tone (probably with an output filter capacitor to "clean
up" the signal). I want to make sure the correct signal is being
received, and I was hoping someone could give me some insight (info, or
even just point me in the right direction with like a book or website).
I also would love to find out more about testing procedures to ensure
the right signal is being received. Thanks for your time, and any
advice is welcomed and appreciated.

Kris