 Why does the narrator reveal his secret ability to Julia?
This being earlier than I usually get up, it seems all I did during the night was feel my way past the escapement and balance wheel to see where the notch for the alarm was. So I'm stuck with a talent I've found little real use for. One went to a battery and the other to hard round cylinders taped together. No, none of them would know it was there. We'd be leaving the valley for the mountain range north of Los Angeles soon, if we hadn't left it already. I'd be a man not to be trusted, a prying man, a man literally with gimlet eyes.
 He needs to stay with the suitcase to keep the bomb from going off. He needs her cooperation.
 He loves Julia, and he doesn't want there to be any secrets between them.  If he doesn't explain his ability, she'll think he's a creeper for going in her luggage.  He needs to stay with the suitcase to keep the bomb from going off. He needs her cooperation.  He'll have a better chance of getting her to believe him than the airport policeman believing his story.