Planet Fitness's 110dB deafening tornado siren. An employee sets it off when they hear weights drop or someone tattles on another member for using a cell phone in the gym area.
The offender is not singled out (and may not even know it's sounding for them).
Other innocent members get blasted with the ear piercing siren, which is above the OSHA sound level limits. The only effect of the Lunk Alarm is to damage members' ears (the employees at the trigger switch are far away from the sound).