Life360 (www.life360.com) has such a feature. It is essentially a safety app so families or groups of friends can keep tabs on each other. Full disclosure: I i

Life360 (www.life360.com) has such a feature. It is essentially a safety app so families or groups of friends can keep tabs on each other. Full disclosure: I interned with them a few years ago when they were a startup out of Berkeley. Looks like they've grown a lot since then.