What to use?

I assume you want some gps tracker that you can carry so family or friend can know your whereabouts at any point in time.

You can buy a dedicated gps tracker and pay the additional fees:
http://www.toptenreviews.com/electronics/gps/best-gps-trackers/

Or consider using your phone and a phone plan as a "gps tracker". Just search the apple app store or the google play store for a compatible app. Just be aware that having your gps turned on full time will eat your battery in a few hours and render your phone useless.

Also consider a "find my phone" type app. I have this feature on a free antivirus app called Zoner (google android). With this app, your family or friend could send you a text with a code. The coded text will remotely turn on the gps on your phone and then send your current gps coordinates by text to the original sender. My thinking is that you could keep in regular contact by calls, emails or text with family back home. If they do not hear from you after a while, they could use this find my phone feature to locate you. Of course, if you get separated from your phone, they will not know where you are. But you would have the same problem if you are separated from the dedicated gps tracker.

Interesting as, according to one of your other posts today, you already have such a device?

"I usually bring a pair of shoes and slippers, some clothes ,phone and a tracking device to keep me on track all the time."

I travel on my own quite often. What is a "tracking device"? If one wants GPS, look no further than one's smartphone even when offline. So I'm confused what else one would need.

And you already have one according to Kathy above? So what is it exactly? :-)