A key feature to look for when buying a handheld satnav.
In an unprecedented total disruption of a fully operational GNSS constellation, all satellites in the Russian GLONASS broadcast corrupt information for 11 hours, from just past midnight until noon Russian time (UTC+4), on 02042014. This rendered the system completely unusable to all worldwide GLONASS receivers.
A military spokesperson for the American GNSS system, GPS, stated that whilst it was highly unlikely this type of complete shutdown due to system failure could occur with GPS it could not be ruled out. More interestingly, he would not rule out deliberate shutdown of the system broadcast civilian GPS signals during times of conflict and actually cited Russia’s incursion into Crimea if escalated could warrant such an event.
Answer: always buy multi-constellation handheld satnav receivers.