A QUICK 40 winks could earn sleepy building watchmen a poke in the ribs from a police truncheon from now on, metaphorically of course. No longer will the protectors of numerous high-rises and commercial buildings in Central be able to prop up walls with their heads or lie full length across two sets of chairs under a blanket. Police officers in Central want more from the watchmen who they believe can be a major help in the fight against crime. And they want a wide-eyed, upright and alert presence greeting visitors in lobbies - not just the soles of feet. More patrols, checking of identities and a general higher standard of vigilance should replace the dreams of green fields and winning the Mark Six, Central District Commander Chief Superintendent Cheung Chi-shum said. ''We want watchmen to contribute more to the prevention of crime. There is evidence to suggest that watchmen making rounds and working more diligently can reduce crime.'' About 40 watchmen attended the first of several seminars at Central police station yesterday and were lectured on crime prevention by officers from the community relations office and intelligence section. Mr Cheung said a recent spate of burglaries in Mid-Levels and at various commercial premises in Central convinced the police it was time to remind watchmen of their responsibilities. ''We gave them a rundown on crime prevention, what we would expect of them and reminded them of their duties. ''It is in fact against the law for a watchman to fall asleep on duty.'' He said officers would wake up watchmen who fell asleep on duty. But one of the most common complaints among watchmen at the seminar was boredom. Some of the watchmen said the seminar helped them - but none admitted falling asleep on duty.