They should fine them an amount that would hurt their pocket if they are caught sleeping or playing with their phones, or just not paying attention. $10,000 per occurrence would be a good start, doubled for each occurance. They should also be limited to the amount of time they are allowed away, and not be paid for the time they spend campaigning either for themselves or other candidates.
Except, politicians don't get rich off their government salaries, but off the various kickbacks, inside information, associated business opportunities, siphoning off their campaign funds or paid speaking engagements. In short, they get paid, maybe $50 K a year, but end up earning tens of millions a year.
In short, they could care less whether they were fined, as long as they could keep sucking up the rich gravy train they create for themselves. They're so busy swallowing up other people's money, they can't spare the time doing their REAL job!