Aerobic bacteria in the filter are dying by the millions when the pump is off. If you can somehow keep the whole system running then the bio system will adjust to the cold and the fluctuation in bio loads year round. I covered my filter falls and it seems to really help keep the heat in since the waterfalls is where most of the heat is released. I use pond heaters because I have a few big pre-forms set up like a brook. One heater is right under the falls to warm the water in the undertow. Another thing I might have to do depending upon ice forms, is to run a dedicated pipe to the filter falls backwards to keep some bacteria alive and add a "T" fitting to divert water directly into the top pond. This way more water and heat will stay in the ponds. Makes sense right? One year I stopped the filter falls for an hour and the pipe underground froze. All I could do was run water into the frozen filter falls and thaw it out in reverse. Water eventually came out the pump connection months later.

At this point, I wouldn't start swapping zones right now - it may just add more confusion. As far as relocating, the sensors can be sensitive to RF interference and, although they shouldn't be, temperature changes on the wall. But first, if you have the installation/service manual - not the owners manual - you can see if zone-4, or all the zones, are "supervised alarm zones/circuits." When I mentioned it may contain a resistor (end of line), it is because of supervised circuits. Supervised circuits, in simple terms, the alarm control panel is acting in a tri-state mode. It it always looking to see a certain resistance across the circuit; let's just say 1k, it's a NC circuit, and the resistor is in series. A cut of the wiring triggers a high resistance error and sets the alarm mode. Somebody who places a jumper across the wiring, triggers a low resistance error and sets the alarm mode as well. The resistor value that must be used will be listed in the installation manual. Since ambient temperature affects resistor values, placement on a wall heated by the sun could cause enough change on a high tolerance resistor to cause an error - but that's just in theory and there's usually enough tolerance in the system, but it could happen. A simple test to help determine sensor, wiring, or controller fault would be to first determine if this is a supervised circuit and it's resistance value. Disconnect zone-4 wiring, at the controller, and either jumper with the appropriate resistor (or just a short wire if non-supervised) and disable all zones but 4. Let it run for a couple weeks and see what happens. Just kind of flowchart logic from there. But actually, I also have another thought here. You mentioned zone-4 is master bedroom and home office, so I'm thinking a PC in the home office... maybe a UPS power supply? Maybe one with an "auto test feature?" I even had an APC unit that by default ran an auto test mode "about every two weeks" - now with the full cycling of the UPS, and it's temperature changes, that could possibly trigger an IR detector... just a thought.

The pic I posted shows my left thigh after surgery for a broken femoral neck bone when I fell only a few feet off a ladder after unsuccessfully trying to use a broom to disengage a battery in a hard-wired smoke detector. I fell onto carpet and carpet pad, and even though my bone density tests showed all was well, and I'm tall (5'9") and in good shape, I must have hit the carpet and pad really hard because it stopped that detector and the others from going off. The detectors had been going off for years, only in the very early morning hours and very late at night only on weekends and holiday since I bought this house in Peoria, Arizona. But no one told me. Not one person, including the sellers, bothered to disclose this. I guess seeing the battery dangling from one of the smoke detectors and wires to electrical outlets in the living room and master bedroom hanging out that the Realtor told me was something the painters did should have given me a clue. But it didn't. I guess I expected that the home inspector -- who I paid -- would have said something, but no. Even when I had no electricity in the living room, part of the kitchen and master bedroom when I moved in, and had to pay a professional "electrician" after the home inspector and Realtor said they were clueless, I still was so stupid I didn't realize that the entire house in this "upscale" section of Peoria, Arizona, had been improperly wired! The detectors would still be going off if the City of Peoria (Arizona) Fire Department hadn't taken them all down cause they were tired of responding and as they said, they aren't electricians. After this major injury and surgery (and a total hip replacement after this surgery failed) since I never cook and don't smoke (nor does my dog), I decided to investigate why the smoke detectors had been going off. I checked to see if they had been recalled, but no. I called the electric company, APS, that serves this part of Peoria (Arizona), but they say there has never been, at any time in history I presume, any problem with their electrical service that could have caused the issue with the detectors. So I believe anything about electricity, wiring, etc., and home systems at this point. When the air conditioning turns on, my Internet service freezes, drops, etc., although Century Link says it "shouldn't". When I shower, when I turn the water to hot (so I guess it uses more of the water heater power?), the lights flicker. The plug for an electric toothbrush I never had any problems with at my old house (in an older part of Peoria that the city allowed to deteriorate even though I asked the city and council for help) began to smolder, smoke and melt while I was out for a few hours (I kept it). So I don't believe what companies, home builders (stay away from TowneHomes aka HBT and whatever else), city officials, building inspectors (approved lots of badly plumbed houses in this part of Peoria), home inspectors, real estate agents, and anyone else says. They don't know anything about electricity, so of course they're going to lie. And if they can get us to keep paying them (monthly bills, taxes, etc.) for lying to us, then the top officials are happy. They don't care about us. I believe all of you with bizarre problems with smoke detectors and everything else electrical. No one knows how to build homes anymore, especially in the U.S., nor do they want to learn. Those who do know don't want to do the job right because it's "too much work". I have never run into so many people in the last several years who hate to "work". I don't know why they don't try to get a job as a sleep study subject. How much work can that be?

Smoke detectors in a garage are generally a bad idea - if you're parking a vehicle in there, the products of combustion are going to trigger it every time. Since it's unheated, that could be an issue too. I personally think some sort of fire detection in a garage is a great idea, but it needs to be a heat detector, preferably a rate-of-rise detector which means you need a burglar alarm (or dedicated fire panel) to connect it to. Even sawdust might set a smokie off, although the new ones seem to be very good at distinguishing these days.