I just examined the Air Alert and was quite dissapointed. It is not very loud, I do not think you will be able to hear it if you are more than 20 feet away from it in dense growth, maybe not even if just high grass. Also, in over half the crashes I've had or witnessed, the battery has become disconnected from the receiver so this (or any other alarm powered through the receiver) would be worthless. To be effective, the alarm must be self powered and a suitably loud noisemaker, preferably an intermittent warble or siren like sound. This requirement means that it will be rather large as the unit must be comprised of the sound making device, a switch and power supply that will last a few hours when needed and packaged in a relatively crash proof case. Of course, in some cases anything might be better than nothing.