The first version of this page ranked three favourites on an engineer's axes: proudest, most inventive, most complex. On reflection, those were the wrong axes. A tunnel between two flats is a Tuesday, and a heartbeat to an external service is a product with a free tier; solid work, but solid work is not what a favourites page owes its reader.
Asked which parts of this we are proudest of, we found we had to answer a different question first: proud on what axis? Not the cleverest, since clever is cheap. Not the most useful, since a light switch wins that. The ones that we have not seen anywhere else, and would not have thought of a year ago.
What it owes is the one axis that cannot be bought: things I have not seen anywhere else. Ranked by that, the list changes, and the former champions move to a shelf at the bottom, which they keep, because they earned it fairly on the old axes.
1. The house with a mood
Everything else here optimises something. Sparky optimises nothing, and it is by our own vote the coolest idea in the house, which for a feature with no function is quite the career.
What makes it original is not the lamp, it is the model behind the lamp: a five-dimensional affect vector (valence, arousal, comfort, sociability, agency) computed from sensors the house already had, plus what is playing, the music's genre and the film's, resolved live, so a horror night reads differently from a jazz evening, smoothed so a mood has inertia, with an episodic memory of when things last happened, and, the load-bearing part, explainable on demand: every dimension shows which inputs drive it and by how much, so when the mood is wrong the argument is about a number you can see.
Commercial “mood lighting” maps a sensor to a colour and calls it ambience. This maps a household's day to a temperament, gives it manners (never touch a lamp in use, stand down for any alert, go dark for an empty room), and lets you debug its feelings. I have not found anyone else doing affective state modelling for a dwelling, with explainability, as a single quiet lamp. It remains the only thing on this site visitors ask about.
2. Sensing a life nobody bought sensors for
Not one detector, a family, all raised on the same question: which signal that already exists changes when this happens? Cooking, from the particulate rise at the nearest sensor. A heated-tobacco session, told apart from cooking by a channel that moves the opposite way: formaldehyde climbs while particulates stay flat, and the general trick, when one channel cannot separate two events, find a channel where they disagree in sign rather than size, is the cleanest single idea this house has produced.
And the third member logs a strenuous and entirely private bedroom activity, in two countries, by the one channel no appliance can counterfeit: carbon dioxide, because an air conditioner can move heat and humidity but cannot breathe. Its ledger is a CSV with a location column and a discretion policy; the site describes the physics and nothing else.
A four-model review panel recently went through every claim on this site; this family came back with two cosmetic caveats, and its anchor sentence was the one piece of physics nobody even tried to dispute. Details on detection.
3. The bank installed a sensor in my wallet
Card payments as a telemetry stream: captured on independent paths that fail differently, watched for silence, because a dead parser looks exactly like a frugal week, and, the part I have genuinely not seen anywhere, treated as hostile input: a merchant name is attacker-controlled text headed for the dashboard of the platform that runs the alarm, so it is sanitised on the way in and escaped on the way out, both ends.
The same well-read panel went looking for prior art and reported that the genre does not contain this page. The build is on money as telemetry.
The engineer's shelf
The former champions, demoted with their honours intact.
The three heartbeats and their truth table remain the highest return-on-effort item in the house, and yes, the mechanics are commodity; the page about them never claimed otherwise. Its argument was always about where the observer stands, not how clever the ping is. The full case, table included, is on the watchman page.
The best single experiment: mapping the wiring by watching a kettle-sized load
Six smart plugs in different rooms, each reporting voltage. Individually that number is useless, it wobbles, it disagrees between plugs, and nobody cares what the mains voltage is.
Together they are an instrument. (An instrument, not protection: the safety framing, what a persistent sag means and when to call an electrician, sits with the method on derived signals.)
First, calibration, because it turned out to be the whole game. At idle, with nothing drawing power, those six plugs disagreed with each other by −0.8 to +1.5 volts. That spread is measurement tolerance, not wiring, and any threshold applied to raw readings would have been roughly half false alarms. So each plug now learns its own resting offset against the median of the others, slowly, and every drop is measured against that plug's own expected value.
Then the decomposition. Take the median drop across all plugs as the common-mode component, that is the incoming supply sagging, and it affects everyone. Whatever remains on an individual plug is differential, that is its own circuit, and it is the part that indicates a problem.
And then the experiment. Switch on a two-kilowatt heating load and watch all six:
| Plug | Change | What it means |
|---|---|---|
| one particular appliance | +2.0 V sag, decaying to 0.7 | same circuit as the load |
| four others, different rooms | −0.4 V | other circuits, the supply barely notices |
| the load's own plug | −0.1 V | …see below |
That is a circuit map of a flat, derived without opening the consumer unit, from hardware bought to switch lamps on. The decay is the thermostat settling into its duty cycle. And the last row is the part that would have caused a wrong conclusion if it had been the only measurement: the plug feeding the load reports almost no sag of its own. Electrically it should see the most, it sits at the end of the loaded branch; that it reports nothing is a measurement artifact of a coarse, filtered meter describing an event it is part of. (An earlier version of this paragraph asserted a mechanism here.
A review panel pointed out, correctly, that a passive plug regulates nothing; the honest statement is that the cause is unconfirmed and the loaded plug's reading is simply not to be trusted.) The practical rule survives unharmed: measure at the load and you see nothing; measure at its neighbours and you see everything.
The plumbing that taught the syllabus
The Belgrade tunnel is, on this review, ordinary networking with an extraordinary lesson plan: three separate layers silently discarded configuration (a consumer router that wipes hand-made rules on any Apply, a container that forgets packet forwarding on every restart, and a routing UI that accepts entries the kernel never creates), and all three failed the same way, the stored configuration said yes, the running system said nothing at all.
Whether these are good ideas is for you to judge. That they are unusual, we can promise; we have looked.
Which is the same idea as the heartbeat, arrived at from the opposite direction. The heartbeat assumes nothing about whether the system is alive and requires continuous proof. The reconciliation loop assumes nothing about whether the configuration is still there and reapplies it forever. In both cases the improvement came from deleting an assumption, not from adding a feature, and in both cases the assumption was the same one: that something which was true when I checked it is still true now.