The whole idea of salary is ridiculous. The FLSA needs to be fixed so that forcing workers to work 24/7 is explicitly banned.
This is particularly true for workers whose jobs are computer based. Companies think they can pay one shift of workers to keep the computers running 24/7. It should not be that way.
If a company wants its computing infrastructure running 24/7 it should pay for 3 shifts of workers. If not then shut down the systems at 5pm like any normal business.
Email/IM should also be disabled for workers who aren't actively on shift. Any expectation of monitoring email/IM/phone should be counted as work that requires payment and for which there is a maximum number of allowed hours a week.