Something made up by the insecure people who run Planet Fitness (Planet Fatness) gyms. They set it off when anyone remotely dedicated to training is in the area. They claim to be a "judgement-free" gym, yet ironically they won't even let those who they deem "lunks" into their facility. The people don't want to "be intimidated" by fit gym goers, yet the only thing intimidating them is their own insecurities.
Planet Fatness Worker: He looks like he might actually be strong and dedicated to his training...what a lunk! Set off the lunk alarm!