The police forensics used my phones and tablets and turned on airplane mode

The police seized my devices and returned some of them to me. I gave them the PIN codes for my devices. Now I see that they have turned on airplane mode... why did they do this? I thought they would connect the device to a computer and look at it that way, not literally use my device to see what I have.

Is it ok for me to use these devices or do you think they have bugged them?

airplane computerforensics forensics mode phones police