In New Zealand, mobile phone coverage is very limited in backcountry areas. While some climbers maintain a philosophy of self-reliance and self-rescue, others don't go anywhere without an emergency communication device. Most people know what a 'PLB' is, but there are a range of other devices available, from satellite phones to devices like a Garmin InReach, which can send and receive text messages, weather forecasts and position information, as well as send an emergency signal. Outside of the add-on features, It isn't always clear what the differences between these devices are in terms of the emergency signal, versus the simpler PLB option.
LandSAR have published a useful article explaining the differences between PLBs, which operate on a cooperative intergovernmental network in over 200 countries and territories, versus the alternative SEND devices that operate on the private, yet global, Iridium satellite network. If you use, or are considering purchasing one of these types of devices, it is very useful information to know.