In remote places, cell phone reception is often non-existent. In an emergency situation, you are on your own without an SOS device. For longer tours it is therefore advisable to purchase one. Apart from the fact that you only have to press one button in an emergency worldwide (where GPS reception is available), some models also allow you to send SMS/emails to contact family and friends. This way, you can turn off the head rush and don’t have to constantly have an uneasy feeling about whether everything is okay at home. You can be contacted in case of an incident. The same, of course, vice versa.
Depending on the model, weather data can also be obtained via the device. In addition, some offer the function of topo maps.
A recommended device for ultralight hikers to not add too many grams to the base weight is the Garmin InReach Mini. It weighs 100 grams without a carabiner. The device connects to the cell phone via Bluetooth. It can be used to write SMS messages on the cell phone, which are then sent via the Iridium satellite network. The connected satellite searches for the next possible mobile station to forward the SMS via the mobile network.
Important: To really use the InReach, a paid subscription is required. The annual cost is about $200 for the Safety Option with registration. In addition, of course, GPS reception is required, which is not given, for example, in caves.