IF you are going to detain someone against their will know your rights, AND theirs cause this is a sue happy state.On that note I was thinking today that my properties should have a RING or equivalent doorbell system that would alert me if there is someone at the door. 

The basic order will be: Domestic violence/emergencies, criminal, landlord/tenant, civil.Emergency breach of lease involving threats or injury to people or property, and emergency wrongful detainer actions trials will begin on June 5, 2020 (Phase II).Rent escrow actions, provided local departments of health are able to provide inspection, tenant holding over actions trials, as well Warrantsof restitution, will begin on July 20, 2020 (Phase III).Civil trials (i.e. post move out collections cases, suits for failure to return security deposits), and Failure to Pay Rent cases will resume on August 31, 2020 (Phase IV).Courts fully operational on October 5, 2020 (Phase V).Rent court dockets are expected to be staggered throughout the day, at least in Baltimore County.

@Erin MaloneYou dont have a lease, so failiure to pay rent would not work.I believe what you need to is wrongful detainer"

Lessee hereby waives all notice of lessors election to terminate this lease or any election by lessor hereunder, demand for rent, notice to quit, demand for possession, notice of breach of any provision herein and any and all notices and demands which may be required by any stature of any state relating to forcible entry and detainer or lessor and Tennant or common law.

I believe it's called "wrongful detainer".

Or where, if I now bought, would there be a legal argument the occupant was unlawfully detaining my property ?

Yesterday I got a letter from a law firm stating that tenant has retained them to address the unlawful detainer action.

Focus on operating the units, aka getting a good tenant in place who WILL pay rents.The eviction path (Unlawful Detainer action) takes about 90days in Calif and may need to get the Sheriff to come onsite. 

Even if they pay (Remember to accept rents with reservations), go to court the next month if they have not paid the debt in full time the court date, get a UD (Unlawful Detainer) but wave the judgement as you expect them to pay.

Here in San Francisco we post 3 day notices after the lease agreement grace period concludes, and if it doesn't cure we file an Unlawful Detainer and wait for MSC (Mandatory Settlement Conference).