After trying several of these devices, this is my favoriate. Works with Electrics, sailplanes and glow planes. I would recommend it to anyone except the 27 MHZ planes that don't have stanard type receivers. For them I recommend the keyringer.

I have this installed in my Glider
http://www.foamfly.com/customer/prod...&page=1&XCARTS
ESSID=247447e257cd206601b76b2716efe0b5
It hooks to any channel or it can share a channel with one of your servos. It
has the connector to pass through to the servo with no impact on the servo.
This will work in any plane with a 72 MHZ receiver.

Low Voltage Watch

In addition to helping me find the planes, this device also monitors
my battery pack voltage and sounds an alarm if the pack voltage gets below a
safe level. This is especially valuable on my glider. If I catch a good
thermal, I could be in the air for over an hour, so a pack that tested good on the ground could run low during the flight.

Channel Conflict Warning!

It also serves as a test to make sure no one is flying on my channel.
I turn on the receiver only. If the device does not go into lost plane mode,
then someone else is on my frequency.