“What’s my responsibility for security at my rental properties?”
The basic rule is that a landlord is required to provide rental premises that are “kept in every part safe for normal and reasonably foreseeable uses.” Practically speaking, this means that if you know about a particular danger or threat of danger, as a landlord you must take reasonable steps to reduce or eliminate that danger.
The real question of course is what are the “reasonable steps” to take? At the basic level, you should make sure that you have adequate lighting that is well-maintained to illuminate the property at night (i.e., replace those burned out bulbs if they are your responsibility). If you have an on-site manager, he or she should conduct a couple of walk-throughs throughout the day, preferably in the early morning and evening hours to note any problems. If you have security doors or fencing, make sure that they are kept in good repair and in working order.
Part of your obligation is to also promptly enforce all tenant rules with written warnings and/or eviction notices if necessary. A good example would be an unauthorized occupant staying with one of your tenants who you have reason to suspect is involved in criminal activity. Even if you don’t have solid proof, you can rely on the fact that the person is not an authorized tenant and evict on that basis alone. You should also immediately evict any particular tenant who is causing trouble. (Hint: Consider a simple no-cause eviction notice.)
If you’ve done all these things and are still having problems (e.g., with suspected drug activity), do you have to do more? The test is what is reasonable to eliminate or reduce the danger. In some cases, that might mean installing security cameras if it would reduce potential criminal activity and it is financially reasonable (and in this day and age, security cameras are relatively inexpensive and easy to install). In other cases, it might be reasonable to install security doors in an apartment complex, for example.
In the end, you will be held to the standard of providing a reasonably safe rental property for your tenants. If you know about a particular danger or potential danger, take immediate steps to reduce that danger. While you can’t eliminate every threat, you can reduce your risk of liability by addressing foreseeable threats.