To have an idea or a lead about something; to have a possible explanation or clue about an event or matter.
鍵をなくしたと言ったら、誰かが見たという心当たりがあるか尋ねられた。
When I said I lost my keys, I was asked if I had any idea who might have seen them.
その時計はどこで買ったか心当たりがある？
Do you have any idea where you bought that watch?
警察が証拠を見せて、容疑者について心当たりがあるかどうか尋ねた。
The police showed the evidence and asked whether I had any clue about the suspect.