The $500 device, which can also play MP3 files, is available from www.randmcnally.com and various retailers.
One is the possible formation of blood clots in the device, which can lead to a stroke.
He would like legislation compelling sellers to ensure that any device which can be connected to the internet is secure.
But neither company could give pricing or a release date for the Plus device, which can be worn on as a bracelet or clipped to your belt.
One tool often used in conjunction with G.I.S. is a Global Positioning System device, which can determine a location by using satellite transmissions.
"What is needed," Mr. Blood wrote, "is a single device which can be used as a computer mouse and telephony handset".
One device, which can be buried near a road, can even discern from seismic readings whether people, trucks or tanks are passing by or approaching.
The device, which can be used manually if a firefighter is lost or trapped, emits a loud buzzing sound if no movement is made for 30 seconds.
The author then strikes it rich by coming up with a device which can be attatched to the dashboard of a car and turns red lights to green.
For some, however, the damage to bone, muscles and nerves from the troubled device, which can shed tiny metallic particles, has left them permanently disabled.
This type of device, which can record high-definition video yet is small enough to fit in a pants pocket, appeals to teenagers and college students who communicate via YouTube, he said.
