Technology very seldom solves social problems. People that perform attacks on civil rights activists usually don't care if something gets public. And even if, it may not have the desired effect: China for example got more restrictive after the Olympic Games brought them bad publicity.
The bracelet just adds a timestamp and a geotag to the ubiquitous message "Human Rights Activist is missing and was probably kidnapped or killed by the oppressors."
We already know all the countries that imprison, torture and kill people because they make use of or propagate basic human rights. But as long as the economical weigh heavier than human rights our governments will smile and shake hands with officials from Russia and China and swallow all the criticism that would be appropriate.

This is a good idea. I think we need a similar system for our children, and scrap the whole RFID chip concept. Hope this saves lives.. or a least gets the 'bad guys' punished.

Giving human rights activists the tools to defend themselves with would do more good.

This article makes me think hard about human rights defenders. The bracelet is an insignia in itself. The concept of activating a wildfire in public outrage appears an effective security device for the people who will use it. Will it be more valued as an insignia?

I don't want to point out a very nasty problem here, what happens if the captors just cut the arm off that the device is on at the time?

Further to an earlier comment involving loss of an arm, what would happen to the electronics if someone were to touch the device with a taser?

I think I see the spirit of the idea. Quoting from Monty Python and the Holy Grail:
"Help! Help! I'm Being Repressed!! Come and see the violence inherent in the system."
It might work in some contexts, especially when attending public protests showing opposition to that protest. It could show which side is really civilized. I think less of the device's effectiveness if the oppressors are inclined to kill the user. It still might work in those situations if the enemy isn't sophisticated enough to overcome it. It would be cool if it also uploaded audio and/or video of the user's last moments. Such content could go viral and bring humiliation to those in power at that location. Its a good tool in the right place.

@flibb - I imagine cutting off a protester's arm would be the worst possible thing to do from a PR standpoint.

In agreement to the first posting, it doesn't matter if the bracelet is triggered, forcibly removed, tazed, or discarded along with a severed limb. All you've done is to note the last whereabouts of the unfortunate individual. It does nothing to prevent the abduction nor prove who the perpetrators are, not to mention being targeted for wearing a permanent "ha ha look at me, I'm a threat to your regime" sign on your wrist.

There are cheap jammers that scramble GPS and cell phone frequencies. Some are designed to use in a vehicle to block any tracking devices or to prevent the use of GPS and phones.
Toss a person wearing one of these bracelets into the back of a truck with a jammer and the signal just 'goes dark'.