Built for the toughest conditions, there’s nothing that can stop the Solara Field Tracker 2100 GPS. Light and portable, the Field Tracker is so durable it can withstand temperatures ranging from -40C to +65C, and works in altitudes of up to 40,000 feet. Able to transmit and receive messages in less than a minute from anywhere where you’ve got a clear view of the sky, this Solara GPS unit will get you out of the stickiest of situations with help from the Iridium Low-earth Orbit satellite system it uses. It costs $880 plus $29.99/month with a 3-year contract for text messaging. Solara Data.