A key card is a card with a magnetic strip that is inserted into a locking device to unlock a certain door or group of doors. Key cards often look much like credit cards, with the same size and shape, along with the magnetic strip along the back side. They are most often used in settings where different levels of security are needed or where locks may need to be changed frequently.

Most people are familiar with a key card from a stay at a hotel. Indeed, the popularity of the key card has nearly replaced all standard locks and keys at hotels in the United States and many other parts of the world. Still, this is not the only application in which they are used.

The key card is also used to provide different levels of security. For example, if one worker has access to part of a building but not another part, there are several ways that could be handled. In the past, workers with extensive access would likely need to carry several keys -- one for each level. A key card could be encoded for access at different levels, eliminating the need for multiple keys.

Some who have received a key card are suspicious that the card may hold personal information, such as names and credit card numbers. However, this is not true, according to John Sileo, an identity theft expert. He notes that the only information usually put on a card is the name, room number and perhaps a partial address of the guest. All other information, such as the guests' financial information, is not placed on the key card but kept in a separate database.

In fact, is is thought that key card security may actually be an enhancement for privacy. Traditional hotel keys usually came with a room number engraved on the key or at least attached to a tag on the key. Anyone who gained possession of the key would have a room number as well. Key cards do not have a room number, but rather usually come in a sleeve with the room number on it, which can be separated from the card.

When you are given card keys at a hotel, it has been run through a programming machine which inputs information onto the magnetic strip. This key card software then sends information to the locking mechanism, which sets a specific time for the key card to work. Usually, the key card will deactivate on the checkout day at or near the checkout time. Those wanting to extend their stay will likely need a new key card with new information. Key card programming is a relatively quick and simple process, so the inconvenience is minimized.