Stair lifts can be a really helpful part of a person's life, as they allow people to get up and down stairs without trouble. Stairs can be very difficult to navigate for some people, like seniors who are prone to falls and more vulnerable to the damage those falls can cause. They are also useful to people with leg and knee injuries, or other permanent disabilities that make going up and down the stairs painful, difficult, or impossible.

Stair lifts are motorized chairs that operate along a track, installed into the the staircase. Often it will run along a handrail or wall, depending on what is available. The individual stair lift will generally vary depending on the equipment available at the time of purchase and the options you choose for safety or convenience. While you can DIY a chair lift installation, it's a fairly complex operation.

Having a regular stair lift installed on a straight stair case with no extra bells and whistles will likely run you between $2k and $5k. This may seem like a lot, but consider that the costs of installing an elevator are much higher (and the construction of an elevator is much more complex) and that otherwise, you or a loved one may not have access to anything but the ground floor. If you have a complicated stairway- like a spiral staircase, or even just one that has turns in it- you will likely end up paying more. You may want to have an estimate done just so you have a good idea of what you're getting into. 

There are a lot of options for extra features on stair lifts. Some will let you install 'overrun' on the track, so that the chair is moved far enough away from the staircase that should a fall happen, it won't involve a tumble down the stairs.

Some also offer more secure stair lifts, where only certain users can access the device- this may be good for businesses, or even homes where you don't want the kids riding the thing up and down the stairs all night.

Chair lifts can be optimized for moving up to 500 pounds in weight as well, so even if you have a family member (or you yourself are) large, you will be able to find a chair lift sturdy enough to suit the needs.

And while most stair lifts are intended for the indoors, there are those that are suitable for use outside. You will have to look around to find what you need.