That really makes me mad. It might not happen again if you ask the manager or rather report to the manager that your missing some cash you had on the counter and you it must have disappeared when people were in your apartment!!!!! What if they would have knocked once (if they bothered to do that) and you were in the shower and then came prancing out in your birthday suit? Who do they think they are? I don't think its legal unless you have given them WRITTEN permission to do so. You should check on getting free legal advice on this. I think you should write and sign a sheet that states that nobody can enter your apartment with out your permission unless a real emergency.