Submit something of importance. Finish a project or one’s results or tools . Suggests you have something that must be taken by hand and given to an authority. For example, The teacher may ask you to  hand in your test after the time limit; the judge may ask you to  hand in your drivers license after getting a drunk driver citation.

“You are fired, Ryan, hand in your pager and leave.”

“I hadn’t finished the test, when the teacher asked us to hand it in.”