To have a reminder means to have something that helps you remember or keep track of something important, like an alarm, a note, or a message. Full definition
Whatever your financial goals, write them down and display them prominently so that you always have a reminder of what it is that you're working so hard for. (clark.com)
Some of the notable bits include a console - based phone charger that also has a reminder in case you forget your phone in the car after parking. (overdrive.in)
It's so easy to forget when I don't have a reminder set! (arteresalynn.com)