THERE IS NO knowing whether the presence of any smoke detectors would have prevented the deaths of five adults and two children in that McLean house fire last week -- but the news of this tragedy has set off useful discussions throughout the region of how and where detectors should be required by local government. In addition, the widespread impact of the McLean disaster has been reflected in a sudden increase in the sales of residential smoke detectors. Though all this attention to the subject is likely to prove fleeting, considerating and enactment of new laws need not be.

What individual homeowners do or don't do about detectors in their own existing single-family dwellings may be their business; but there is more than common sense or privacy involved when it comes to rental and multiple-unit housing or new and remodeled structures. Yet in Virginia, some property owners and developers persist in portraying such safety requirements as violations of individual rights and/or sources of unnecessary economic hardship.

That's nonsense, for not only can they be held responsible for certain life-saving measures, but smoke detectors are no longer all that costly. When introduced about 15 years ago, most devices sold for about $100 apiece. But today, experts at the National Bureau of Standards noted that most of the detectors now selling for $10 to $15 are quite effective -- capable of detecting nearly invisible levels of smoke.

Under Virginia law, the devices are required only in residences built since the state's building code went into effect about five years ago. But not, at least, the Fairfax County Board of Supervisors is studying ways to stiffen legal requirements. Unfortunately, some steps may require approval by a traditionally reluctant state legislature. As part of the local effort, though, the supervisors already have voted to ask insurance companies to offer financial incentives to policyholders who install detectors.

Montgomery County requires that detectors be installed in all residences regardless of the ages of buildings. And a similar measure is scheduled to go into effect in the District next year. Other area jurisdictions should also act -- without waiting for another terrible fire to spur the efforts.