What are these?

[Kent Keith]

On one of today's inspections were these devices and was not sure of exactly what they were. The house was built in 1976 and these were in each bedroom where the smoke detectors were usually mounted and one in the attic mounted on a collar tie. I tried to take that one apart, but could not figure it out. They have no electrical wiring. They have a metal tab on the left side that when pushed, sets off a bell ringer inside, like a test button. On the right side was a red lever marked "rewind" as to rewind a spring for the bell. The only thing I could think of was some sort of fire heat detecting mechanism, but if this is what they are, then it seems like it would be a little late for the occupants before they would sound.
Does anyone have any info on them?

[Gunnar Alquist]

Kent,

I once saw a mechanical heat detector that looks mighty similar to the pics that you posted. Not sure how it was triggered, but you actually had to twist the outer housing to wind-up the spring mechanism.

[Jerry Peck]

What are these?

Antiques. :)

Replace with interconnected smoke detectors.

If no wiring is present, install interconnected battery operated wireless ones.

[Jim Luttrall]

Yep, heat detectors.
We had a discussion on these a while back, I think.
My brother tried selling a similar product back in the late 60's to early 70's. Same principle as a sprinkler system, melting sensor sets it off.

[Rick Cantrell]

Kent
As others have said, those are mechanical heat detectors.
They are not necessarily old, as some are still being manufactured and sold. They can be quite pricey, but are nearly worthless. The problem I have with them is that people have a sense of being protected, but in reality, they have almost no protection.
As Jerry recommended, replace them with interconnected smoke alarms.

FYI The test button does not test the detector, it only test that the bell operates.

[Jerry Peck]

As others have said, those are mechanical heat detectors.


You mean "mechanical alarm" heat detectors, right? ;)

[Rick Cantrell]

Jerry
Somehow I overlooked your post untill today.

"You mean "mechanical alarm" heat detectors, right? "
Point taken. Since it is an all in one package
(detector, sounder, and power in a self contained unit), and not the detector only, that does make it an "Alarm", but I think it would be described as a "Mechanical, Heat Alarm".

[Jerry Peck]

"You mean "mechanical alarm" heat detectors, right? "
Point taken. Since it is an all in one package
(detector, sounder, and power in a self contained unit), and not the detector only, that does make it an "Alarm", but I think it would be described as a "Mechanical, Heat Alarm".

Rick,

I worded it the other way to designate what it was, and what it is likely called, it is a "mechanical alarm" "heat detector".

What it is not is a "mechanical detector", it simply has a "mechanical alarm" which is activated after the "heat detector" senses what it is set to sense, and that triggers the mechanically wound, spring loaded, alarm.

Thus, I believe it is most correctly described as a "mechanical alarm heat detector" (smoke detector, whatever the detector was).

A mechanical alarm would be like a string tied under tension to an anchoring point and a trip lever, which burns in two, and allows the alarm to sound. :D

[Rick Cantrell]

"A mechanical alarm would be like a string tied under tension to an anchoring point and a trip lever, which burns in two, and allows the alarm to sound. "

I agree, and a good description of how they work. Heat melts a plastic or metal substance, which releases the drive mechanism that strikes the bell.

"What it is not is a "mechanical detector",

It is not electronic, so if it is not "Mechanical" then how does it operate?

[Rick Cantrell]

Sorry
I put the emphasis on mechanical, but now I think you meant the emphasis to be on Detector.

[Jerry Peck]

"A mechanical alarm would be like a string tied under tension to an anchoring point and a trip lever, which burns in two, and allows the alarm to sound. "

I agree, and a good description of how they work. Heat melts a plastic or metal substance, which releases the drive mechanism that strikes the bell.

I suspect that heat does not melt anything, if it did, those would not be re-usable (not without replacing the fusible link), in which case I suspect the mechanical alarm would not be easily rewound simply with a lever accessible from outside the unit.

How they operate is unknown to me.

They may indeed be "mechanical" in the operation of the detector, but ... see my comments above.

[Jim Luttrall]

As stated that is a fire alarm. Purely mechanical. Winds up just like a giant clock spring. That small metal button in the center is made of "Woods metal". It has a very low melting point. Same metal they use on sprinkler systems at the sprayer nozzles in the ceilings. Once it melts there is a tiny wire plunger that pops out in the center then all hell breaks loose.
This from another board concerning a similar product.

[Rick Cantrell]

All heat detectors that I know of, are one time use, even the ones I install.*
There are heat detectors that have a feature called "Rate of Rise". RoR, as the name implies, detects how fast the temp rises, in addition to tripping the alarm at a fixed temp, it trips the alarm when the temp rises fast enough. The RoR feature can be used more than one time, but the heat detection part can only be used once. Also the RoR feature can be mechanical or electronic.
* On second thought, I think some combo Smoke, Heat, and RoR detectors may be all electronic.