Each time I was putting my cell phone on "vibrate" to be considerate of others or in situations that require it, I was forgetting to turn the ringer back on. Therefore I was missing calls until someone brought it to my attention that I wasn't answering my phone. So now when I put it on this quiet mode, I take a stretchy ponytail holder and put it around my car keys. This serves as a reminder to switch my phone ringer back on, as I can't go anywhere until my keys are free!