The previous entry on this project is here <link>.
I worked on this project earlier this year and put it into daily service back in April. The batteries died last night (this morning) at 4:00 AM, earlier than expected. They lasted 5.5 months and had the same rapid decline to 2.7 volts that I saw when I was running it in accelerated mode to understand how to do this.
Basically they coasted along dropping a little over time and then just dived, relatively speaking over a couple of weeks to a level where it wouldn't work anymore. This seems to be the normal behavior of alkaline batteries, so nothing new.
I am disappointed that it took less than six months to die though, but it died two days after my TV remote control died and I changed those batteries around the same time as this device. I remember because of the coincidence of having the remote need batteries around the same time as I started the long term test on the sensor. Could be the life of the cheap batteries I'm using.
The device was set for 115 seconds off and 5 seconds on and I can easily change that to a much longer off period if I need to, but I'm not sure I want to. Having the temperature available at two minute intervals is nice and fits with my longer term plans for temperature control in the house.
On the reliability front, this thing has worked day after day without a hiccup. I use it to turn off the bedroom and outside lights when I go to bed every day and sometimes just to show it off. Never gave me a problem unless the controller it talks to was having problems because I changed something there. It's still a bunch of components on a proto board though. I couldn't find an enclosure to fit it that I liked and decided to wait until I could buy a 3D printer to make something for it.
My tractor and the terraforming work around the house ate up the money I was setting aside for the printer and that has been postponed until I finish that stuff. Keeping flood water out of my house and repairing ruts in the driveway will always take precedence.
I put some more of the exact same batteries in it, and it's beside the bed again doing exactly what it's supposed to. I'll check on it from time to time and see what develops over the next six months or so.
Maybe by then I'll have an enclosure for it.