Can your landlord just waltz into your apartment without notice

Nobody talks about how many landlords act like they own your space the second you sign the lease. I’ve heard horror stories—people coming home to find their door unlocked, or worse, their landlord "just stopping by" unannounced. Isn’t there a law against this?

I’ve been renting for years and always assumed 24-hour notice was standard, but apparently not everywhere. Some states barely require any notice at all. What’s the deal? Anyone else dealt with this nonsense?