Every so often, whatever my family is doing stops because Detective Jev's light has gone yellow or red, and we go and check what it's worried about. It turns out to be one of the sliding doors open on a cold day, or the front door open for too long, or something like that.

Detective Jev is our version of TypeSafe's Jev, the model for fast, typed decisions that I used in Jev Atlas. It is a small app I built with AI help that runs beside Home Assistant, keeps checking our house through the day, and tries to tell us when something is out of the ordinary.

It doesn't have enough data on our house yet to be very smart. For now it is about as smart as our dog, who barks at the mail delivery person.

Detective Jev's page in Home Assistant on a phone: a cut-paper Sherlock Holmes smoking a pipe, a green label saying All as usual, and the line An evening at home. The same page with Sherlock Holmes pointing, eyes wide, a red label saying Needs you, and the line The dining room's sliding door is open, for 46 minutes; nothing explains it.
Detective Jev's page in Home Assistant, calm, and then worried about the dining room's sliding door. Family details are taken out of these screens.

On its page, Detective Jev is a little cut-paper Sherlock Holmes. Its mood also shows on three LEDs on a breadboard, driven by an ESP32 running ESPHome.

An ESP32 development board on a white breadboard, with jumper wires and three LEDs at the bottom left; one LED glows green.
The breadboard while Jev is calm, so the green light is on.

How Detective Jev decides

Through the day, Detective Jev lists what's going on in the house, and next to each thing it puts whatever might explain it: what Home Assistant's logbook says caused it, the automations that act on it, how often it usually happens, and our notes. TypeSafe's Jev decides which of those explains each thing, if any, and how urgent it is. Detective Jev only speaks up about what nothing explains, so the backyard lights coming on at sunset are never news. What it finds sets its mood.

  • Detective Jev smoking his pipe.All as usualGreen light
  • Detective Jev shining a torch.Worth a lookYellow light
  • Detective Jev scratching his head under a question mark.A reading doesn't add upYellow light, blinking
  • Detective Jev pointing at an exclamation mark, eyes wide.Needs youRed light
Detective Jev's four moods, drawn and animated as on its page, and the board's light for each.

The first version didn't know what caused anything, and it was worried most of the time. It flagged the backyard lights 27 minutes after sunset because they "usually last 12 hours".

Talking to Detective Jev

The page has a chat, answered by OpenAI's GPT-5.6 Luna, and that's how we change what Detective Jev does. What we tell it becomes a note that it reads the next time it looks. The chat can't switch anything in the house, only change what Detective Jev knows: add or forget a note, add a check that should always hold, or stop watching a device we don't use any more.

On Thanksgiving Monday, with several doors open and several burners on, I told it that this should be reported. It asked whether that held every day or only on weekday late mornings, and saved the note when I said all the time.

The Talk to Jev part of the page: my message that many doors open and many burners on should be reported, Jev asking whether that applies every day, my answer, and Jev's reply with a green Noted label.
The chat, with my note about doors and burners.

I wanted TypeSafe's Jev to do most of the judging, because it is cheap, so GPT-5.6 Luna only runs when we talk to Detective Jev, and once a night.

Detective Jev dreams

Each night, Detective Jev "dreams": GPT-5.6 Luna consolidates its notes. It merges duplicates, keeps the newer of two notes that disagree, drops expired ones and keeps each note short. Any night's changes can be undone from the page.

The What Jev knows part of the page: folded rows for Notes, Expected and Not watched, and the Changes row open, listing the nightly tidy at 03:30 and an earlier shortening of 15 notes, each with an Undo this button.
What Detective Jev knows, with each night's tidy and its Undo button.

The other night, before he went to sleep, my young son asked me if Jev was green. I told him yes, he's green, and everything is fine.