Colleague Dave LeRoy bought a Casady smoke detector recently and was filling out the warranty card when I dropped by to see him on some National Press Foundation business.

"I'm impressed." I said. "I admire your patience. I don't think I've ever filled out a warranty card in my life."

"Why not?" he asked.

"Oh, I don't know," I said. "They always ask a lot of irrelevant questions and I just don't have the time to fool with them."

"This one is no different," Dave said. "They not only ask what model I bought, where I'm going to use it, what kind of home I live in, and how many people are in the household, but they want a lot of highly personal information as well. For example, they want me to put my age, my wife's age and my annual income on the postcard. Can you imagine anybody giving that kind of information on a postcard? And they also want me to state whether my home is protected by a burglar alarm system."

I looked at the card and noted some of the other questions. "Did you buy this unit as a gift?" "Is your home equipped with a fire extinguiher?"

Dave read my mind. "That's not just a registration form," he said. "It's also designed to give them some valuable merchandising information. It tells them what kinds of people buy their product, and for what reasons; and ir also gives them an insight into the sales potential in related items like burglar alarms and fire extinguishers, and builds their mailing list."

"Well, if I had the time, I wouldn't mind giving them some types of mechandising information," I said. "But I certainly wouldn't be fool enough to disclose on a postcard what types of security systems my home does or doesn't have."

"Me either," Dave said. "But now that I have bought one of their products, it occurs to me that perhaps I'd better fill out their warranty card. If I don't, they may give me the merry ha-ha if the detector ever needs repair service."

A good point. Does the consumer waive his right to a warranty or limited warranty if he doesn't fill out the registration card and return it to the manufacturer?

About two days after my conversation with Dave, the married woman I live with called me at work and announced, "Our smoke detector is driving me nuts. It keeps sending out screeches every minute or two. The little red flag pops out to say the battery needs changing, and I don't know how to shut it up. I push the little red flag back in, but a minute later it pops out again and the detector sends out another screech."

When I got home, the smoke detector was still yelling for somebody to change its battery, so before I could even pour myself a glass of beer I had to tend to it.

I removed the battery and checked it on my battery tester, which is not really designed to handle 12.6 volt batteries. My tester has only four settings: 1.5, 6, 9 and 15 volts, so I tried it on 9 and on 15.

On 9, it almost knocked the needle loose from its moorings. On 15, it was in the "good" range. The next morning, a friend with a professional battery tester checked my battery and found it full of life.

Reluctantly, I headed for the General Electric small appliance facility in Georgetown. I felt guilty and was mentally prepared for a hassle because I had never filled out the warranty card on my smoke detector - and I just knew that would be the first question they'd ask me.

The clerk was a man I had never seen before. I didn't know him, he didn't know me. I handed over my smoke detector and said, "The battery is good. I tested it. But the alarm keeps beeping and the 'change battery' flag keeps popping out."

Without a moment of hesitation or indecision, the clerk nodded understanding. He disappeared into a back room for about five seconds and returned with a brand-new unit. "If the battery is all right, the sensor must be out of whack," he said. "I hope this new unit won't give you any trouble."

I walked out in a daze. "I wish Dave LeRoy had been here to see this," I said to myself.

It's so nice to know that a few old-fashioned principles are still being respected by Big Business, and that limited warranties are not always limited to what's in the small print.

A tip of the hat to the General Electric executive who figured out that there is no long-term profit in making customers angry.

I wish we had a lot more like him.