Thermometer-based alarms are useless because they routinely go off
during the automatic defrost cycle.
The problem with the makers' "door open" alarms are that they work on
the hinge side so they're spectacularly inaccurate. What's needed,
*obviously*, is a switch at the opening edge of the door. But it seems
to be beyond the wit of the manufacturers to understand that or to put
it into practice.
I did try making my own "door open" alarm many years ago, using a timer
operated by a microswitch stuck on the side of the cabinet with a lever
between the cabinet edge and the door seal. I can't remember why but it
wasn't very successful, probably not robust enough for a kitchen
I wonder if some sort of magnetic detector might work better - there
are, after all, magnets in the door seal. Or perhaps a low-profile
keyboard-type switch between the cabinet edge and the seal? Or any other
How about one of the window burglar alarms sensors that uses a magnet
and reed switch?
> Door wide open when I'm rearranging stuff? Beep beep bloody beep, yes,
> thank you, but it's obvious the door's open isn't it?
No cancel button?
> Door half an inch open because one of the drawers isn't quite pushed
> home? Silence.
> Thermometer-based alarms are useless because they routinely go off
> during the automatic defrost cycle.
Don't be such a lazy B and buy "frost free" heaps of shite then. The
important thing *is* the temperature if that rises for any reason you need
to know about it. Must admit if the frost free thing doesn't "know" it's
doing a defrost cycle and can supress the alarm for the expected duration
plus a bit it is poor design.
Actually I'd also like a to low temp alarm as well. When we bung 3 loaves
of bread in the freezer it alarms due to the temp rise. Put it into "rapid
freeze" mode but then forget about it until I spot the display showing
Its simple enough if you can do some electronics. A metal foil contact
on each face, but not used as a swtich, rather used as a detecting
capacitor. An oscillator uses those contacts as its frequency
determining capacitor. Door closed, C higher, f higher. Output from
osc goes thru cap and is threshold detected. You also need the circuit
to detect correctly if the foils connect, so provide a dc path for
that condition too.
Now, with door open/closed reliably detected, its up to you to add
whatever suppression you want, eg timer, cancel etc, and whatever
output you want, eg LED while not closed, and beeper if not closed for
3 minutes or more.
If you cant do electonics... youre stuffed.
Excellent idea - and not too conspicuous if mounted *under* the door. I
can't imagine why I didn't think of that, because I recently designed
some very effective LED drawer lights using exactly what you suggest. I
even know where to get the right sort of switches, with contacts that
*close* when the magnet is withdrawn (the opposite of what's needed for
It might be a bit of a fiddle getting the range right but it's a very
promising idea. Thanks.
Well, we've got it now. And it's attached to the fridge that we rather
like. And it's a non-standard cabinet size that just happens to suit our
kitchen rather well. So we're in no hurry to swap it.
>important thing *is* the temperature if that rises for any reason you need
>to know about it. Must admit if the frost free thing doesn't "know" it's
>doing a defrost cycle and can supress the alarm for the expected duration
>plus a bit it is poor design.
Now there's a thought. I was about to counter that it's the temperature
of the food that matters, whereas a short increase in air temperature
(which is what the alarm is responding to) is of little consequence.
It's an aftermarket alarm, which obviously doesn't know when the defrost
Answer: wrap the sensor in a little insulation (e.g. put it in a food
container) to shield it from short-lived temperature rises. I'll get
onto that straight away. Thanks!
But an effective "door not closed properly" alarm would be much better.
>Actually I'd also like a to low temp alarm as well. When we bung 3 loaves
>of bread in the freezer it alarms due to the temp rise. Put it into "rapid
>freeze" mode but then forget about it until I spot the display showing
Here's your answer...
I can do the electronics at a pinch, but I was hoping for something
simpler, that didn't involve running a wire to the door or a constant
battery drain. Thanks for the thought.
Its not a FIsher & Paykel one by any chance?!?
Some years ago (prolly about 20), I made one for Mum's freezer. I got
the innards out of a musical birthday card, a miniature microswitch and
a small piece of wood (as an actuator for the microswitch). I glued the
card innards and the microswitch on the side of the freezer and the
wooden block on the edge of the door. OK, you had to listen to the tune
incessantly whilst the door was open, but the problem (of leaving the
door slightly ajar) went away. The battery in the card outlasted the
Nowadays, of course, musical birthday cards are bases around digital
samples, so they don't play annoying monophonic tunes that keep going
I think youre out of luck then. Sticking extraflex to the underneath
edge of the door shouldnt be hard.
> or a constant
> battery drain. Thanks for the thought.
why would one run it off a battery?
If you want a simple switch in series with a beeper, you could do that
but dont expect decent performance.
>I've had several freezers with "door open" alarms but they've been all
>been f***ing useless. Door wide open when I'm rearranging stuff? Beep
>beep bloody beep, yes, thank you, but it's obvious the door's open isn't
>it? Door half an inch open because one of the drawers isn't quite
>pushed home? Silence.
I had one for a fridge which was a red plastic apple shape
incorporating a light sensor. I don't know if the leakage around
a freezer door slightly open would be enough for it to operate.
Chris J Dixon Nottingham UK
Have dancing shoes, will ceilidh.
Give that man a cigar!
But there's the same problem with our other freezer (Zanussi) and its
I bought a Candy fridge freezer a few years back and cursed it more
than one because the magnetic seals weren't very and the freezer
door would bounce slightly open if you didn't pay attention.
The fix was easy but only realised it when I got my new fridge here.
Just make sure that there is a slight rearward tilt thus making the
door self closing. Not 100% re a drawer left open of course.
>> Actually I'd also like a to low temp alarm as well.
> Here's your answer...
Hum, two things to ponder. What is the range like with the transmitters
inside an earthed metal box, I notice that they mainly stress having the
display on the fridge/freezer. Also what batteries do they use for the
unit in the freezer, most batteries don't like much below 0C let alone the
-18C or more of a freezer.
Tiny current consumption when in sleep, hall effect should work with the
door strip and you can make the sensing range adjustable in software.
Parts cost probably under a fiver too. Anyone interested?
Your scepticism does you credit. :-)
>What is the range like with the transmitters
>inside an earthed metal box, I notice that they mainly stress having the
>display on the fridge/freezer.
Mine works through the front door of the freezer and then 2.5m across
the kitchen to the side of the other freezer. I haven't experimented
>Also what batteries do they use for the
>unit in the freezer, most batteries don't like much below 0C let alone the
>-18C or more of a freezer.
ISTR they recommend lithium. Not many places stock lithium AA so I
ordered some from CPC. While waiting for those to arrive I put in some
ordinary Duracell alkalines (both sensors). That was at least a year or
two ago and I haven't needed the lithiums yet.
I doubt many people are set up for PICs. A single hex invertor chip
would probably do the lot.
Did that with my Hotpoint once. I don't know how low it went, but it
was below -40C where the mercury (or red stuff) went off the scale as
it all went into the thermometer bulb.
[email address is not usable -- followup in the newsgroup]
When we open our freezer the light comes on!
Maybe tie something into that? Perhaps a bell-transformer that will
send low voltage to a buzzer and/or light elsewhere.
>When we open our freezer the light comes on!
But when you close it are you really sure it goes out?