A chaperphone is a good friend who can't come along on a date or other activity, but will call you or text you at least once, but often multiple times, to make sure you're not in trouble.
I have a blind date tonight, and I think it's going to be awful. Will you be my chaperphone and call me or text me at 9 so I have an excuse to leave? or... I know I'm married, but I want to hang out with this hottie tonight. Will you chaperphone me every half hour so I stay out of trouble?
*See Also Phoneperone Pronounced Sha-per-phone, a person you call and talk to while in an unfamiliar or scary place. In theory the Chaperphone can send assistance to you if a situation arises.
When my wife crosses a dark parking lot she calls me because I am her chaperphone.