and used as indoor wheelchairs. Outdoor stair lifts Outdoor stair lifts are available for straight and curved staircases. They operate similar to indoor stair lifts but include weather-resistant features to help the unit withstand extreme harsh temperatures and weather conditions. Most often, outdoor stair lifts are used on staircases for decks, home entryways or lake access. Previously owned stair lifts There is a second-user market for some types of stair lift. This is most common with straight rail domestic types. The rails can be cut to length if too long, or extended with a "joining kit". Most models allow the carriage to be "re-handed" so it can be used on the left or right side of the staircase. During the early days of curved rail stair lifts there was no second user market because of the difficulty of matching rails to a different layout. Even staircases built to the same design specification in neighboring houses have variations, but in most attempted "transplants" there are too many differences to make it practicable. Many owners have had to pay to have unwanted curved stair lifts removed. More recently, some curved rails have been produced to a modular design so components can be unbolted and used elsewhere, subject to design and safety considerations. In some cases, tubular section rails which are welded during manufacture, are produced by specialist rail companies so they can be used with a previously owned carriage, controls, and other components. This is, perhaps, like putting an old locomotive on new railway lines. It provides a lower cost solution than buying a totally new system. Some insurance companies have offered breakdown policies for stair lifts. Manufacturers and installers have offered an extended warranty, rather like those available for domestic white goods and brown goods. Goods stair lifts Some manufacturers produce stair lifts with trays instead of seats for moving goods between different levels, usually in commercial or industrial buildings. Some businesses have purchased normal domestic stair lifts purely as goods transporters and put items such as boxes of stationery on the seat. AC and DC power Early stair lifts mostly had alternating current (AC) drive motors which ran at full mains voltage (around 115 volts in North America, 230 volts in Europe). An "energy chain" ran alongside or through the rail to carry the power cable from the supply point to the carriage. More recently, domestic stair lifts have been