Green’s Dictionary of Slang

(US) being inattentive, not concentrating on a task.

[c.1875		G. Hoey ‘Asleep at the Switch’ [ballad] Murdered by one who should guard them from harm, who now lies asleep at the switch].
[1894		Red Cloud Chief (NE) 25 May 4/4: Recitation ‘Asleep at the Switch’, by S. Frisbie].
1899		W.J. Kountz Billy Baxter’s Letters 40: Along about twelve o’clock I thought I would talk over old times with Bud, but when I turned his way I found my tried and trusty comrade ‘Asleep at the Switch.’.
1902		‘Hugh McHugh’ Back to the Woods 11: I fell asleep at the switch and somebody put the white lights all over me.
1915		Van Loan ‘On Account of a Lady’ in Taking the Count 137: You’ve been asleep at the switch a long time, but you’re waking up now.
1920		W. Williams What’s on the Worker’s Mind 198: The club dues are continuous, unless the barkeep is too busy, or asleep at the switch.
1922		Wash. Times (DC) 15 Oct. 10/2: Up to this time I think I had been figuratively ‘asleep at the wheel’.
1934		Wodehouse Right Ho, Jeeves 97: My guardian angel had not been asleep at the switch.
1953		J. Thompson Criminal (1993) 49: Telling him he was asleep at the switch.
1994		G. Hamel Competing for the Future 299: Most of the casualties come when a company crashes into the future, with top management asleep at the switch.
2007		W.E. Griffin Hunter 481: We ran into him at the Petroleum Club yesterday and, if I hadn’t been asleep at the switch, we could have had him and his family here tonight.