Schlage is one of the most popular brands of consumer and commercial locks in the United States. They have been in business since 1920. They provide a wide range of locks for commerical and residential installations including the high-security key and cylinder lines, Primus, Everest and Everest Primus XP.
Check your key chain and look for a key that looks like this. Chances are you have a Schlage lock at your home or office.