Datalogic Falcon X3 Quick Reference Manual page 9

Shift the cardholder to the left and then pull it up; insert the SIM Card with its contacts downward
4.
and its round corner at the bottom:
Lock the card into place by pushing the cardholder down and then shifting it to the right.
5.
Pull the locking plate down.
6.
Close the battery cover properly, by pressing the latch release button and pulling the latch down.
7.
Follow proper ESD precautions to avoid damaging the SIM card. Proper ESD
precautions include, but are not limited to, working on an ESD mat and ensuring that
the operator is properly grounded.
CAUTION
Do not force the card. If you feel resistance, remove the card, check the orientation,
and reinsert it.
Do not use the SIM card slot for any other accessories.
The SIM Card option is not available in
802.11b/g radio and batch models.