Here in California, the law requires that all homes have working carbon monoxide detectors. So I headed out to my local Home Depot and picked up a combo fire and CO alarm.
When I got home, I removed the packaging, but I couldn't separate the unit from its base. Assuming it must be defective, I returned it to Home Depot and picked up another one of the same model. This time, I wanted to make sure I could remove the unit from its base before heading home. I opened the package, and I still could not separate the unit from its base. Some Home Depot employees said they had the same problem with the product.
At this point, I read through the manual, and it turned out this particular model had a feature that was supposed to prevent closure of the unit when batteries were not installed. Could this be the problem? I looked the unit over and, through the slots in the base, saw a latch in the battery cavity. When I pushed this button in (as it would be with a battery present), I was able to remove the base.
On further inspection, I realized that the design of this feature actually had the opposite effect as intended. The angle of the knob (attached to the latch) that was used to prevent closing of the unit without batteries actually allowed the base flange to ride over it, locking the unit into the base without batteries.
Once the base and unit were closed, this feature actually prevented opening it again if batteries were not installed.
Now just imagine what would happen if the base were installed in a wall or ceiling before the batteries were placed in the unit, and then you attached the base to the unit. You would end up with a useless alarm, and you wouldn’t be able to remove it without breaking it apart.
This entry was submitted by John Muren and edited by Rob Spiegel.
Tell us your experiences with Monkey-designed products. Send stories to Rob Spiegel for Made by Monkeys.
This is a perfect example of the need for PLM systems to bring in the important voice of the customer to the design and production functions. In an earlier story Beth Stackpole covered the move to bring service into PLM: http://www.designnews.com/author.asp?section_id=1394&doc_id=239660
Bringing in the voice of the customer may also big a huge help.
This tale is one more example of the futility of attempting to protect stupid people. On quite a few occasions some stupid interlock designed to prevent one action winds up preventing some other action, until the interlock function and hardware is removed, completely and positively bypassing whatever intent was in the original design. Of course the fact is that the less skilled person would probably do much more damage to the product while removing the interlock function.
I believe code now requires that all smoke/CO detectors in new homes receive line power, trigger all other detectors, and have a backup battery. You cannot put a stand-alone smoke/CO detector in new construction. You can buy wireless alarms and use them to replace older "solo" alarms. That's what I'd do in a home without hardwired alarms.
The law is probably in the way of making this easy - what I mean is that the usual 9V battery for the smoke alarm makes it a stand-alone device that anybody can install at their ceiling. As soon as you make this device use grid power to avoid the use and requirements of replacing batteries, you are immediately confronted with either:
- use a power supply and a wall/ceiling outlet and run the cable to the smoke detector, a pretty ugly solution but if you can install near an outlet it could still be a customer installable device
- attach the detector to the house wiring, which should require an electrician, though this is a permanent solution and you never have to change a battery again. It can be costly though to run wires, install an outlet and connect each alarm to it.
If you want to go for a system that sounds the alarm in all rooms when there is a problem in one location, then you will need either wireless or the grid connected alarms which have an additional wire installed to communicate with each other and set of the alarm on all units
In a previous century I got so fed up with buying and changing batteries that I used a rechargeable battery and trickle-charged it directly from the grid through two very high value resistors that constantly replaced the fractional mA consumption plus self-discharge, so I never had to worry about it again until I moved out of that house, many years later.
I have seen many smoke detectors, have been installing them in my house since some 20 years. All follow the same essential basis rules, including the *inability* to close the cover when there is no battery installed, to avoid malicious people from making it "look good" without actual battery as well as to force/remind you to purchase a new battery (after it started beeping in the middle of the night and you yanked the battery out) for that dangling-open smoke detector...
Having a detector that not only closes without battery but even locks you out unless the battery is already installed is exactly what you don't want and a typical case of a design spec saying "must have locking feature" and the engineers faithfully implementing each of the line items. I have seen a lot of specs that in their context were not ambiguous, but when read line by line, you could clearly see how the engineers implementing the literal text of the spec got it exactly reversed. This product is yet another example of such. The product should not be sold if the store is aware of the problems with it though.... That is just bad service to your customers.
I think it's more likely the designer was confused as to which direction the alarm screwed into the base. If I could figure out how to upload pictures from my PC, I'd show you...
It is interesting reading all these threads. I suggest you read the book "poorly made in China". I have worked directly with our suppliers in China and there is a good correlation between my experiences and those quoted in the book.
You're right, Rob, you can probably multiply this by a thousand. What always amazes me is that there are so many of these kinds of problems, and that it takes so long for companies to notice them -- or, more accurately, to admit that the problems exist.
I'd like to offer an alternative to this being a poor product design. It is entirely possible that the design was validated and performs as intended, however, a manufacturing blunder may have caused the problem. If the injection mold was not assembled correctly then the latch could have been molded with the ramp on the security tab facing the wrong direction.
I have seen/heard of many injection molds where the inserts are not keyed to prevent improper assembly. The mold may have been assembled properly for the design validation and acceptance run only to later have been taken apart for maintenance and re-assembled wrong.
Many years ago I read an article in the long-gone industry newspaper, "Electronic News." It seems a fire broke out at a... now wait for it... smoke-detector manufacturer! To save consumers time, the company preinstalled the battery or batteries. When the firefighters arrived the noise from all the screaming alarms was so loud they had to let the fire burn itself out.
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