What are the laws concerning someone who rents a home and is the landlord of the home allowed to come in at any time?

Laws will be different from country to country, and possibly even from state to state in the US. I think virtually everywhere in the US, a landlord does not have the right to enter a rented (up-to-date) property at any time. Your rent doesn't give you full ownership of the property, but it does give you certain rights. The privacy of your home is something you should be able to expect when you rent and are current. The landlord does own the property, however, and has the right to inspect the property after giving you adequate notice (and possibly under other circumstances according to the law). You'll have to check local/state laws.