He was sent out to take care of a breach in the basement of the Clamp Center, which was Billy Peltzer and Kate Peltzer who had broken in to cancel the sprinkler system which could get the Mogwais (who had already formed cocoons to transform into gremlins) inside wet.
As the security guard approached, Kate hid and the security guard then confronted Billy, having him at gunpoint and insisting on taking a look inside Billy's bag, suspecting the man to be a terrorist. Billy said that he wouldn't look in the bag if he was the security guard, but the guard looked either way, whereupon the mogwai Daffy who was in the bag, jumped at the security guard and bit his nose. The guard yelled in pain and stumbled around a bit while Daffy was biting his nose before throwing the mogwai away and firing his gun at it, but Daffy escaped unharmed. Billy then tried to warn the guard that there was gonna be more, but the guard angrily took Billy with him to the police station, ignoring the warnings. It is unknown whether or not he survived the gremlin invasion of the building, however it is likely that he did.