Once aboard the plane you turn on the receiver and watch the 4 red lights turn green as signals are received from each piece of luggage:

A red light (for #1 above) indicates that a bag is out of range and that it didn't make it on the plane.

I made the housings from black acrylic with clear fronts to show off the circuitry inside so that potential investors could see the simplicity of the design, and the 2 coin type Lithium batteries.  Also see that transmitters #1 and #3 use external antennas that I added later to try and extend the range of the devices, the other units use miniaturized internal antennas.

My client is an air line pilot and said this about working with me:
"I thought you did a great job, and equally importantly had integrity in our dealings.  If you need to use me as a reference please feel free, I'll be glad to tell anyone the same."
His email address is: JoelWire@compuserve.com