1. To turn off some piece of machinery or equipment with or as with a key. A noun or pronoun can be used between "key" and "off." Two people have to key off the reactor simultaneously. He sat in the car with the engine idling for several minutes before he finally keyed it off.
2. To cause someone to be aware of or suspicious about something; to tip someone off. A noun or pronoun can be used between "key" and "off." The user's description of the problem keyed me off that there was likely a problem with the servers. The boss's strange demeanor keyed off staff members that there was bad news on the horizon.
3. To use a particular piece or source of information as the basis for some function, action, thought process, etc. The program's algorithm keys off the user's library and recent activity to create music recommendations. We had been keying off of an outdated data sheet, so we had to spend the entire next week inputting the information all over again. Everything the system processes is keyed off the bar code on the product.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.