How to Stop Trespassing on Commercial Property in California
Updated: 3 days ago
To stop trespassing on commercial property in California, post clear no-trespassing signs, secure fences and gates, file a notarized trespass authorization letter with your local police or sheriff, and have security staff document and report repeat trespassers. Since January 1, 2024, those letters can stay in effect for up to 12 months instead of 30 days, which makes enforcement much easier for owners who are not on site.
Key takeaways
California Penal Code section 602 covers most trespassing on private property, and subsection 602(o) lets an owner authorize police to act when the owner is not present.
Senate Bill 602, effective January 1, 2024, extended trespass authorization letters from 30 days to up to 12 months and requires them to be notarized, according to the Alhambra Police Department.
Signs, fencing, lighting and locked gates make trespassing harder and support enforcement.
Security guards can ask trespassers to leave, document repeat visits and call law enforcement, but they should not use force to remove people.
Industrial and warehouse properties, like many in the City of Industry, benefit from a mix of fencing, patrols and cameras.
What counts as trespassing on commercial property in California?
Trespassing in California generally means entering or staying on private property without the owner's permission or refusing to leave after being asked. Penal Code section 602 lists many forms, including refusing to leave property that is closed to the public or posted, and occupying property without consent. Most commercial trespass cases are misdemeanors.
For business owners, the most common situations are:
People sleeping or camping in loading docks, alcoves or vacant buildings.
Loitering in parking lots after hours.
People cutting through fenced yards or climbing onto roofs.
Repeat visitors who were told to leave before.
The details matter. A store that is open to the public is different from a fenced industrial yard that is closed to the public. Talk with your attorney about how section 602 applies to your property.
What is a trespass authorization letter, and how do you file one?
A trespass authorization letter, sometimes called a letter of agency or trespass enforcement authorization, is a signed form that allows police or sheriff's deputies to enforce trespass laws on your property when you or your agent are not there. Under the current rules, the letter must be notarized and can last up to 12 months.
The Alhambra Police Department describes a typical process:
Download and complete the agency's trespass authorization form.
Complete a separate form for each address you want covered.
Sign the form in front of a notary.
Submit it to the agency, and deliver or mail the original if required.
Calendar the expiration date and renew before it runs out.
Each agency has its own form. The City of Industry is served by the Los Angeles County Sheriff's Department, so owners there should contact their local sheriff's station for the correct process.
Which physical steps reduce trespassing the most?
The physical steps that reduce trespassing most are clear signage, sturdy fencing with locked gates, bright lighting, and removing places to hide or shelter. These make your property harder to enter and make it obvious that people are not welcome after hours. They also support enforcement, because posted and closed property is easier for law enforcement to act on.
| Step | Why it helps | Cost level | |---|---|---| | No-trespassing signs at every entry | Puts people on notice | Low | | Fencing and locked gates | Blocks casual entry | Medium | | Motion-activated lighting | Removes cover of darkness | Low to medium | | Trimmed landscaping | Removes hiding spots | Low | | Secured dumpsters and alcoves | Removes shelter | Low | | Cameras with signage | Evidence and deterrence | Medium |
Check fences and gates every week. A single cut section of fence can undo the rest of your work.
What can security guards legally do about trespassers?
Security guards in California can ask trespassers to leave, explain the property rules, document each contact and call law enforcement when someone refuses. Guards can make a citizen's arrest only in limited situations, and most companies tell guards to observe and report rather than physically remove anyone. Clear post orders keep guards within the law.
A guard's job on a trespass-prone property usually includes:
Checking fence lines, docks, roofs and alcoves on a schedule.
Politely asking people to leave and offering local resource information when appropriate.
Writing a daily activity report with times, locations and photos.
Keeping a log of repeat trespassers to share with law enforcement.
Calling 911 for any threat, fire or medical emergency.
For a deeper look at the limits, read what security guards can legally do in California.
Should I use a patrol or an on-site guard for trespassing problems?
Use random patrol checks when trespassing is occasional or happens mainly at night, and use an on-site guard when trespassers return daily or the property has high-value equipment or vacant buildings. Many industrial owners start with patrols, then add on-site coverage at the worst hours if the problem continues.
Vehicle patrol service works well for large lots and multiple buildings, because patrol officers can check fences, gates and docks several times a night at unpredictable times. Overnight patrols are available in many areas; contact us to confirm.
What should property owners in the City of Industry do first?
Owners in the City of Industry should start by walking the property at night, fixing fences and lighting, posting signs at every entry and filing a current trespass authorization letter with the sheriff's station. Then decide whether patrols or a guard are needed based on how often trespassers return.
A 30-day plan:
Week 1: Night walk-through, list of damage and hiding spots.
Week 2: Repair fencing, add lighting and post signs.
Week 3: File the notarized trespass letter.
Week 4: Start patrol checks and review reports.
Learn more about our security services in the City of Industry.
Frequently asked questions
How long does a trespass letter last in California?
Since January 1, 2024, a trespass authorization letter can stay in effect for up to 12 months. Before that, the limit was generally 30 days.
Does a trespass letter need to be notarized?
Under Senate Bill 602, yes. Agencies such as the Alhambra Police Department require the signed form to be notarized before they accept it.
Can a security guard remove a trespasser by force?
Guards should not use force to remove trespassers in normal situations. They ask people to leave, document the contact and call law enforcement if someone refuses.
Do I need no-trespassing signs on my property?
Signs are strongly recommended. They put people on notice and support enforcement on property that is closed to the public.
Is trespassing a felony in California?
Most trespassing on commercial property is a misdemeanor under Penal Code section 602. Some related conduct can carry more serious charges.
About the author
Samantha Stephens leads SGV Patrol, a security company serving the San Gabriel Valley since 2012. SGV Patrol is Licensed, BSIS PPO #17353. You can verify our license on the California DCA license search.
Get a trespass prevention plan for your property
Dealing with repeat trespassers? Call SGV Patrol at (626) 727-1592 for a security assessment. Calls are answered 24/7.
Sources: California Penal Code section 602; Alhambra Police Department, "Trespass Enforcement Authorization" (alhambraca.gov), accessed November 4, 2026. This post is general information, not legal advice.
Cover photo: "City of Industry, CA, USA" by peter boy12qq12, via Wikimedia Commons, licensed CC BY 3.0.
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