beats me
phr. “(the answer is) not known to me.” (The emphasis is on me.)I don't know the answer. Beats me!Beats me how those things stay in the air.
Don't ask me.
sent. “I don't know either.” (With the emphasis on me.)I don't know. Don't ask me.Don't ask me. I wasn't there.
for all I know
phr. “as far as I know”; “I really don't know.”For all I know, they just did it for a lark.She came in late because she had an accident, for all I know.
not know beans (about something)
tr. to know nothing about something.Don't pay any attention to her. She doesn't know beans.I don't know beans about fixing cars.
Search me.
sent. “I don't know.” (There is a heavy stress on both words.)Tom: How do crickets make that chirping noise? Bill: Search me.You can search me. How should I know?