legal except in regards to audio and that is different for each state. In Louisiana it is only legal to record conversations if you are one of the parties. So you can record your phone conversations but not your spouse.
and of course it depends on where you put them. No cameras in bathrooms or change rooms is obvious I’d hope.
i completely missed the part where OP wanted covert. Most of that stuff comes from China and is dirt cheap. But you may want to buy two of everything since there are lots of duds. There are online spy shops but much of it is even on Amazon now. Many interesting built in options that are built in to light bulbs or surge protectors. And you could not tell without disassembling.