Just bought a gun? Don't have/can't get a concealed firearm permit (CCW)? Here's how to open carry safely. Be sure to check out the open carry page on where you can and can't carry.
Though handgun snatchings from citizen carriers are statistically rare, they do happen and most often they happen to ill-trained and ill-equipped new carriers. Another common danger is a loose holster letting your gun spill out on the ground with your body movements; few things reduce confidence in an open carrier than a gun skittering across the store floor when you reach for the bottom shelf. A good holster will keep your gun where it belongs on your hip.
Friction retention relies on the tightness of the holster material itself to keep the gun in place. Originally, this was just tight leather. Holsters made of modern materials like Kydex and polymers hold the gun fast with retention screws. These tighten the fit of the holster against the gun by twisting the screws.
One Level Retention
I'm defining each level of retention as one level, with friction only being "zero."
The most basic form of active retention, that is where a mechanical device affirmatively holds the firearm in the holster and must be deactivated before drawing, is a simple strap. This type of holster is common for revolvers, 1911s, older style semi-automatics, and people who just like that kind of thing. These types of holsters have a button snap that can be popped off with the thumb, allowing the hand to draw the weapon.
Next we have a locking holster, such as the Blackhawk Serpa, which is a poor choice because the finger releasing the paddle can, under stress, contact the trigger resulting in an unintended discharge. A better choice is the Safariland ALS series, where the thumb releases the locking mechanism when grabbing the pistol's grip. These types of holsters are best for civilian open carriers.
Two and Three Level Holsters
These models have multiple levels of redundancy and are best used by law enforcement, which faces a much higher risk of gun snatchings than average citizens do. The below Safariland holster has a strap locking system that must be disengaged during draw, but also has a hood that prevents the pistol from being drawn except from behind (by the officer).
Don't Carry Like This
Always get a holster, never carry tucked into your belt or in a pocket. Carrying like this makes you look like an amateur and that can embolden someone to snatch your gun. This is the equivalent to a little old lady leaving her purse in the shopping cart while she turns her back on it in the grocery store in the bad part of town. Don't look stupid.
Also, not carrying in a holster can result in negligent discharges. Many people have been shot by pistols when holstering them because clothing or some pocket item contacted the trigger as the pushed down on the gun to snug it into whatever. Don't shoot yourself; get a rigid holster that covers the triggger.
You should always be paying attention to your surroundings. At home? Pay attention to strange noises or voices. Out in public, be sure to look at people. That suspicious guy? Look him in the eye. Don't just put your head down and look at the ground or get lost in your cell phone.
Thieves target easy targets. Someone who is unaware is an easy target because the attack can begin before the person starts to react. Check out Col. Jeff Cooper's color codes.