An alarm in your head that goes off when someone around you lies, compelling you to yell "BULLSHIT!" suddenly and loudly.
When Tina heard Dylan say he aced the Geometry exam, her bullshit alarm went off, and several teachers frowned disapprovingly when she yelled "bullshit!" in the hallway.
by Rose Reaper October 29, 2007
When someone tries to tell you something that you know is not the truth, it is an "alarm" that goes off in your head telling you not to fall for the lie.
I was at the dentist's office and they were selling me something at a high cost that I did not need. My bullshit alarm went off that day, and I got red-faced with extreme anger!
by Julius Wrightmoore June 4, 2021