An investigator is hired by a landlord to investigate a tenant suspected of illegal activities within their rented unit. What is the legal limitation regarding entry into the unit for surveillance purposes?

1. The investigator cannot enter the unit without the tenant's consent or a court order, even if the landlord consents, as the tenant has a reasonable expectation of privacy.
2. The investigator can use a covert camera installed by the landlord prior to tenancy.
3. The investigator can enter if the landlord provides a key and consent.
4. The investigator can enter if they suspect illegal activity is occurring.