I used the SPOT Satellite Messenger during my hike of the Arizona Trail last spring, and wanted to let you know what I experienced using the device. Weighing 7.3 oz (including two lithium batteries), the SPOT device is billed as “Handheld satellite communication and safety device” by SPOT Inc. (a subsidiary of Globalstar, the satellite telephone company).
Power SPOT on, and the onboard GPS chip goes to work determining your location. Press one of the three transmission buttons, and SPOT will attempt to transmit a signal to the Globalstar satellite network, with the unit’s unique id number and the coordinates of your location packed into the transmission. This information is directed to ground-based antennas and then forwarded to appropriate recipients on the ground via email or emergency service notification.
Transmission button choices include “OK”, “HELP” and “911”. After subscribing to the SPOT service and setting up your account, you are given an opportunity to provide email addresses for up to 10 contacts who receive email notices when the OK and HELP buttons are successfully activated. These email messages include a prewritten text note that you, the subscriber provides, as well a link to Google Maps indicating your position as determined by SPOT’s GPS chip. Should you press the 911 button, the subsequent satellite message is directed to local emergency and rescue services. The company claims a “99% or better probability of successfully sending a single message within 20 minutes” using SPOT within their designated coverage areas around the globe. Pretty slick.
My primary motive for using SPOT on the Arizona Trail was to have a simple way of letting family and friends know where I was on a daily basis. I transmitted twice a day; once during lunch and again at the end of the day when I arrived at camp. I took care whenever possible to put my SPOT into its “OK” transmission mode for at least 20 minutes each time I transmitted.
Unfortunately, SPOT cannot tell you whether a transmission has been successfully received by the satellite and ground system. This is because SPOT is a one-way device; it can only transmit messages skyward, it cannot receive messages from the satellite system above. On my trip I soon learned that my transmission success rate was somewhere around 80%. I speculate that the failed transmissions were due to an inadequate view of the sky because of trees and other overhanging vegetation, or being confined by canyon walls or nearby hillsides. (For additional information on maximising transmission success rates, check this 1/26/2009 post.)
Knowing that about 20% of my transmissions failed, I took care to tell family and friends not to worry if they did not always receive messages from me when expected. In a situation where I might need to use the “911” or “HELP” button, I think I would go to the trouble of transmitting multiple times from different locations if there was any doubt about how good a view of the sky was available.
In spite of the missed transmissions, we were all delighted with messages that did get through; SPOT really can be a good way to keep in touch with people when you are out in the wild. When relying upon SPOT in an emergency however, I think it important to keep its limitations well in mind.
I worried about SPOT getting jostled or compressed in my pack as I hiked, possibly triggering an unneeded rescue effort. So, for peace of mind I removed one of the batteries from my SPOT before stowing it away in the pack, and I took care to carry extra batteries in case I lost the battery I had removed.
By the way, here is the text of the email message that my SPOT transmitted when I reached the end of the Arizona Trail:
SPOT "OK" check in for Dave Baker
Nearest Location:not known
Time:05/15/2008 16:29:56 (GMT)