'Teen Mom' Star Amber Portwood -- STRICT Home Detention Rules

Amber Portwood's home detention rules are so strict -- HOW STRICT ARE THEY??? -- not only is she barred from drinking alcohol ... but she can't even use mouthwash that contains alcohol or eat foods containing alcohol. Kiss that rum cake goodbye!

As TMZ first reported, the "Teen Mom" star was denied entry into a halfway house because they thought she'd be a bad influence on the other residents. So now Amber is on home detention with her grandparents until a new drug treatment program accepts her.

But this isn't your typical trip to grandma's house. According to the rules laid out by the Madison County courts ... Amber, since she is without a job, must remain inside the home at ALL TIMES unless she gets prior authorization (even then it has to be for things like AA meetings or attorney appointments).

The rules dictate she can't consume alcohol or illicit drugs, but the no-no list also includes non-alcoholic beer, any medications containing alcohol (R.I.P. NyQuil) and the aforementioned mouthwash or foods that contain alcohol.

Amber also has to have a working phone at all times and she has to be the one who answers, should the home detention people come calling.

If she violates any of the rules ... it's back to jail for her.