Cozumel is safe
Crime
The US Department of State does not name Cozumel in any travel advisories
The local crime rate is lower than US cities of comparable size
We do not worry about walking around Cozumel at night
There is no local "narcoterrorism" threat
Almost all crime is theft rather than violent crime
Use common sense
Lock all doors doors (house, car)
Use the security system
Don't leave valuables unattended outside the house
Don't let anyone but our maid and staff in the house
This includes your divemaster or that great guy you met at that place
This is for both your safety and ours (to prevent someone returning later to break in)
There may be exceptions if we know your intended guest
Tell us whom you'd like to invite and we'll let you know
There are people on the island we'd trust to the ends of the earth
Don't give anyone your door/alarm code for any reason
Anyone who's authorized to be in the house will already have their own individual code
Police presence
It's common to see state, federal, or military police patrolling with assault rifles or shotguns
This is meant to make their presence seen and to be reassuring
Police normally drive around with their lights flashing all the time
This does not necessarily mean they're responding to a crime or pulling you over
Traffic Safety
Traffic presents the biggest safety risk to Cozumel visitors
Do not rent scooters
Don't speed
Do not rent scooters
Pay attention to one-way streets
Do not rent scooters
Do not drink and drive
Do not rent scooters
Look out for "topes" (large speed bumps)
Do not rent scooters
If you must rent scooters, don't ride them
Weapons
Mexico is very serious about controlling weapons. Do not bring them.
In particular, do not bring any firearms or ammunition at all. You're likely to end up in jail if caught.
Avoid carrying pocket or dive knives around town, as these can be determined to be weapons