L.B.
First alert makes door alarms that are really easy to install (uses an adhesive already on it) They are really loud! They also have an on/off switch so you can have it active only at night. I come from a family of sleepwalkers and my 15yo son does it so I feel your pain. He once sleepwalked into his sister's room then jumped off the top bunk onto the hardwood floor. The worst is when he would sleepwalk at sleepovers, one of the parents caught him trying to get out their back door where they have a pool. I still get chills thinking about how that could've turned out.