As landscape photographers we often spend extended periods of time in remote areas that are devoid of a cell signal, by nature most landscape photographers like their alone time, being alone is not a way to keep safe in the wilderness. What would you do if you were injured and could not evacuate yourself? Hope somebody comes by? I would not call that a plan!
My choice is carrying a Personal Locator Beacon, these devices are GPS enabled and have a homing beacon to help rescuers find your exact location. I did extensive research and found the ACR ResQLink to be the highest recommended due to its very small size and features. Along with the GPS and homing beacon it has a strobe light to aid in rescue. The battery on this device is rated to last 10 years, and if you ever have to use the device, they will replace it for free! This is meant to only be used once in the most dire of situations, meaning you will die if you do not use it. If you have a sprained ankle and fight through the misery of hiking back, do not push the button. If you cannot walk, but are not in a life threatening situation you don't press the button. A rescue will cost a small fortune and it puts the rescuers life at risk, this is only for life and death situations! The ResQLink appears expensive on the surface, but the beauty of it is that there is no yearly fee.
Another option is a different class of devices like the Spot, these are very common and some models allow you to send text messages or status updates to facebook. There are some downfalls, like a yearly fee, and as you add features this can get quite expensive. If you have a worry wart back home this may be a great way to ease their mind. Another problem is battery life, since these are a dumb-ed down satellite phone you do have to replace the batteries, personally in a life and death situation I don't want to run the risk that I didn't replace the batteries. These also work off commercial satellites which has close to worldwide coverage, but may not be as reliable as the ResQLink which works off of government satellites. Another similar device is the DeLorme InReach, which allows 2-way communication with your loved ones.
Finally, you can use a satellite phone, which works off the same networks that Spot and DeLorme use. These can have long delays when connecting to satellites though, but still a potential solution. They are extremely expensive and require paid monthly subscriptions which are also expensive.
The ResQLink sends a signal 10 times stronger than the Spot or DeLorme and is the most reliable for being rescued. There have been confirmed cases of a Spot not sending an SOS or not sending correct GPS coordinates. I know which one I will trust my life with.
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