Backstory: I'm a gym rat and love randomly meeting up with friends in the gym. I'm lazy too, but only some kinds of lazy, I'll go to the gym but I won't text my friends... you're the same, don't lie ;)
The Idea: Share your "I'm at the gym" beacon with you friends when you hit a geofenced area, the gym. You don't want your friends knowing where you are every second of the day but a quick "hey, I'm at the gym, would be awesome"
Deep Dive: This one is hard to get deep on, you could pivot into a dating app where you would be alerted if there were more guys/girls in the gym. Don't get creepy.
Validation: This would be a fun one, I popped this question to my gym friends and they were all in!
Monetization: I feel this would be a free app with an ad banner at the bottom and $1.99 to remove ads. This is not my idea scenario but not all can be unicorns, this may help pay the bills.