Lipo alarms that are a few bucks usually have a fatal flaw. They go off as soon as a battery dips below 3.1v/cell (or whatever it's particular rated voltage is)... but readings of the voltage of a lipo while firing the gun regularly go under 3.0v/cell when firing, when the load is suddenly applied to the battery and then released, it returns to the higher resting voltage.
So you need a computerized alarm that will ignore sudden peaks/troughs and only read resting or rms voltage.
But, as long as you're running a computerized alarm, you may as well have a low voltage cutoff as well... and at that point, you should have spent as much money getting it set up as just getting a computerized extreme-fire mosfet with low voltage alarm and cutoff built in which vibrates the motor to alert you to it's condition.
