How much notice does my landlord have to give before entering my unit?
Most states require advance notice — commonly 24 hours, and 48 in a few like Delaware and Hawaii — plus a valid reason (repairs, inspections, showings) and entry at reasonable hours. A handful of states have no statutory notice rule and leave it to the lease. A genuine emergency, such as a fire or burst pipe, lets the landlord enter immediately with no notice.
If your landlord enters repeatedly without notice, document each instance; depending on the state it can amount to harassment or a breach of your right to quiet enjoyment, and may support a habitability or privacy claim.