The Nordic-proprietary %XPOFWARN command controls the power off warnings from the modem. The command is supported by nRF9160 SIxA B1A.v1.1.x≥3v1.2.x≥1v1.3.x
%XPOFWARN is based on voltage level detection without any delay. When this
warning has been sent once, it needs to be enabled again by sending
AT%XPOFWARN=1,<voltage>.
%XPOFWARN is enabled by default at the 3000 mV level. Active %XPOFWARN warning blocks the storing to NVM.v1.3.x≥2
For a detailed description of the nRF9160 power supply monitoring functionality, see Power supply monitoring in nRF9160 Product Specification.