An arm restraint for restricting movement of a person's arm during sleep. The arm restraint includes a lower strap, an extension part coupled to the lower strap at one end of the extension part, the extension part including an adjusting unit for adjusting a length of the extension part, and an upper strap coupled to the extension part at another end of the extension part. The lower strap is wrapped around a lower part of a person's body. The upper strap is wrapped around an arm of the person's body. The extension part is sized by way of the adjusting unit such that the arm cannot abduct above a shoulder level of the person.