u-blox SARA-G3 Series System Integration Manual page 46

SARA-G3 series - System Integration Manual
 High logic level at SIM_DET input pin is recognized as SIM card present
The SIM card detection function provided by SIM_DET pin is an optional feature that can be implemented
/ used or not according to the application requirements.
u-blox AT Commands Manual
For more details on SIM detection function refer to the [2], "simind" value
of the <descr> parameter of the +CIND and +CMER commands.
UBX-13000995 - R06 Objective Specification System description
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