Your marriage certificate has to be attested by the embassy for your sponsor(s) to accept it. Everyone in your HR depts would know you are not married as would many of your co-workers in your accomodation.

Is it possible to fly under the radar? Possibly if you never make any enemies at work or your home. If your employers find out you will probably be terminated. If a neighbor complains to the police the consequences are going to be more serious.
The police do not go looking for you but they act on complaints. Lots of people live together but you need to be aware of possible serious problems.