Voxengo Beeper

Beeper is an auxiliary audio processing plugin which you can use to insert short beep, noise burst or silence signals to any sound material.  This plugin may help you protect your work from unauthorized use.  It is safe to apply this plugin to any mission-critical material because plugin does not perform any processing on the audio between the inserted signals.

You may specify signal’s duration, beep frequency, signal’s loudness, period between signals and the amount of random variation of all parameters.