Good old pagers. I absolutely don't miss mine, but they were a welcome relief to get the odd message when you were working in dangerous or "clean" environments where phones (or any other electronic or transmitting device) were prohibited.
I think my last one fell out of my belt and into a toilet mid-piss, so that was that.
I had one briefly when I was in high school. Between school, extra curriculars, and two jobs I was never home to get calls so I kept it so that if my friends had something planned after I got off I could get into some trouble. This was before cell phones were small enough to be practical.
Unfortunately some folks that didn't like me got ahold of the number and would blow it the fuck up while I worked so I got rid of it and my friends started leaving notes under my windshield wipers when they'd go out.