Our product of choice for your standalone electronic access project is the Alarm Lock DL2700 Trilogy. It installs for a fraction of the price of hardwired keyless access systems. If you're on a tight budget, this may be the product for you.
The unit seen here is the weatherproof model, which means it can be installed outside. This unit is on the door of a chemical lab of a business in Manchester, Tennessee. The DL2700 keyless access product can hold up to 99 different user codes. It has a key override as well. What's really great about this product is that you can easily program it to stay unlocked if you want. You can also add a one-time user code and lock out everybody's codes on Friday night and reinstate them all on Monday morning. If you have to delete a user code for some reason, you can do so easily. Programming is simple, and the unit comes with an easy-to-understand programming manual. There are other models in the Trilogy line that can be programmed with your computer, and others that can be used with a key fob.
Another wonderful option you can consider is a remote release switch. If you have a medical clinic and do not want to get up and unlock the door from the waiting room every time the doctor calls, consider a remote release. The remote is wireless and can easily be installed. You can add more than one release button if you wish.
What about durability? I installed one of these at Prescotech in Murfreesboro, Tennessee. The company is no longer at that location, but the unit was installed on an outside employee door. The unit lasted for 14 years! And - get this - we replaced the batteries three times! This, I will say, was an unusual occurrence for a lock installed outside without any protection whatsoever. On the other hand, I have seen a very few last for three years. However, the product is low maintenance.
The DL2700 uses AA batteries that are housed in a special plastic container. The product also has a restore-to-factory-settings feature which you can use to erase everything and start fresh if you need to do so.