There are currently (2016) two consumer-facing easy-to-obtain devices that you could use for this, although they don't quite transmit in real-time (they'll transmit updates down to every 2 minutes).
They both work in a similar fashion: utilizing a combination of GPS to calculate your location and the Iridium Satellite communications network to transmit it (so it doesn't rely on cellular signals and has global coverage), they transmit on an interval you decide to a website that your interested party could monitor.
The two devices are: Spot Satellite Communicator and the DeLorme (now owned by Garmin) inReach.
This isn't a free service, there is a monthly fee for both devices.
In July 2016 ($USD)
inReach: Allows tracking updates every 10+ minutes ($15/month) or the 99/month package allows for updates every 2+ minutes.
Spot: 50/year allows 5, 10, 15... minute tracking update intervals or $150/year: 2.5+ minute tracking updates.
DeLorme inReach:
Spot Satellite Personal Tracker:
