Schematic Diagram

Parts List:
R1 = 2M      C1,C2 = 0.01uF (10nF), Ceramic
R2 = 47K     C3,C4 = 2.2uF, Tantalum (or electrolytic)*
R3 = 4.7K            tantalum was chosen for its weight.
R4 = 10K        Q1 = NTE159, PN200, *BC557(a), 2N3906, etc.
U1 = LM555      Q2 = NTE123AP, PN100, *BC547(a), 2N3904, etc.

U1, the timer/oscillator IC, LM555, NE555, SE555(c), NTE955, ECG955, etc. 
The CMOS version of this IC (MC1455P) uses only 1/10th the current!).
3 volt buzzer, servo connector to fit your receiver pack (optional).
Final Notes:
Most every R/C'er knows how hard it is to find a crashed or downed plane in high grass, thick brush, corn or soy fields. Many aircraft are probably still laying there waiting to be found. This circuit will help you to find your aircraft/rocket easily. It is easy to build and does not require special parts. Using replacements is just fine. If you opt for a seperate 9-volt battery (don't forget an on/off switch) the buzzer should be approx. 6-volt. Do *NOT* connect the + of the 9-volt battery to your receiver! Serious damage will occur! In my prototype I put silicon gel arround all the electronic components, immediately put the hole thing in heat-shrink and left to dry overnight. It now is vibration-proof. The circuit was still working when my Goldberg Falcon Mark III folded the wings from a height of about 400 feet and slammed into the ground (at full trottle) and dug itself in almost 6 inches deep.

Just in case you're wondering how to hookup the 9-volt alkaline battery: Fig. 2    The negative (-) of the 9-volt battery and the rx-battery pack are tied together.
Keep in mind, if you hookup the battery incorrectly you may damage your receiver, so be careful. Can you use the receiver's battery power? Yes ofcourse. It will just drain your receiver battery a lot faster. If you are into slope soaring, gliders, or any other area of R/C with long-duration of your radio/receiver batteries, I strongly recommend to use a seperate 9 volt battery. To save on weight, NiMH would be my choice. It is true 9-volt versus NiCad being 7.2 volt.

A transmitter provides every 20 milliseconds a set of pulses, which in turn sends your receiver a seperate pulse to each of the servos at the same interval. The circuit above is a so-called missing-pulse-detector. An alarm will sound when your receiver no longer receives the set of pulses from your radio. So, to locate your aircraft, all you have to do is switch your transmitter off and the locator will start to beep. Easy huh? If you wish, you may even use point-to-wiring on vero board or something. The tantalum capacitors are polarized so watch the + and - sides. This circuit works best when just plugged into an empty position of the Receiver. I do not use the 9-volt battery setup myself, since I only fly 15 minutes with my heli at a time.
If you need more information and data on the 555 timer/oscillator IC.
*CAUTION: The European BCxxx type transistors have their emitter/collector reversed in most cases. Check for proper pinout first to make sure it is so.

This device is tested for interference with JR, Futaba, HiTec, Airtronics, and ACE radio equipment. None were found and none are expected when used with other brands of Radio equipment.