As the global demand for safer cars grew, there was a drive for cheaper and more accurate ways to deploy airbags.
Thus, car manufacturers turned to MEMS based accelerometers and gyroscopes. Small, accurate, and fast.
With increased production, comes increased manufacturing efficiency. So these sensors also became cheap to purchase for everyone.
In this case, phone manufacturers looking to differentiate their products started adding gyroscopes. Now your screen could automatically rotate when you moved the phone!!!! And there were also benefits for inertial navigation, controlling games, silencing the phone when it was face down, and all sorts of other things. Yay!
Because every phone includes a dozen different camera lenses, it's now cheap to stick cameras where they never went before:
You have an accelerometer in your phone because air bags became mandatory.
Soon, everything will have a camera. pic.twitter.com/jwApIDM8Nc
— Terence Eden (@edent) April 7, 2015
So why not a bidet with a butthole-targeting camera for extra precision? Or a bird's-eye camera above your stove so you can see when a pan is boiling over? Or a fridge-cam so you can check if you need cheese when you're out shopping?
Adding WiFi to a product costs a couple of quid. The cost is insignificant for most consumer electronics.
I recently saw a "Smart" water bottle. It had a sensor to tell you how much water was in the bottle, a temperature sensor, an accelerometer to determine when it had been picked up, and a wireless comms module to send that data to your phone.
The price? About US$20 wholesale.
It's slightly silly, sure. But its usefulness is also slightly above zero.
As USB became the dominant way to connect peripherals to computers, the plugs and sockets became cheap and ubiquitous. Now everything charges via USB.
And, sure, WiFi is a bit power-hungry - but throw in a USB socket, or a Qi charger and you've solved that problem. Or use BlueTooth Low Energy / Zigbee / LoRaWAN.
Low power devices can harvest "waste" energy from movement and heat.
About a million years ago, my undergraduate dissertation was on Ubiquitous Computing. I (foolishly) took out a section about a smart toilet-roll-holder which automatically ordered more paper as it was getting low. And a smart toilet which called the cops after detecting illicit substances in the user's urine.
Adding sensors and transmitting that data is cheap. For all the jokes about WiFi fridges - I'd quite like my dishwasher to send me a push notification when it is done. And, yeah, I wouldn't mind if it ordered new salt and rinse-aid when it is running low.
An ultrasonic sensor in my recycling bin's lid would let me know that I shouldn't bother going outside because the bin is already full. It could even form a mesh network with the other bins to let the refuse collectors know how busy they'll be each morning. Perhaps it would refuse to open if I tried to add something which didn't have an RFID chip indicating its recyclablility.
Digital photo frames with a built in lens could do facial recognition of the person looking at the photo - and can then display the photos best tuned to them.
Shoes which know how many miles you've walked - and can discreetly alert you to foot odour.
A jacket which has a large flexible display to show people what cool music your phone is sending to your headphones. And a camera on the back to snap photos of people who are checking out your arse.
A sensor in your stomach that tells you that it was last night's leftovers which gave you gas.
A sensor in your belt that tells you your bladder capacity isn't sufficient for the rest of the movie you're watching.
Paving stones which report footfall - and light your way back to your car. You follow the yellow-brick road, I'm following the pulsing polka-dots.
Socks which send little beeps when they are more than a few meters from their matching pair.
Toys which report back to the manufacturer exactly how long they're played with. And what demographic of child uses them most.
Every door hinge recording their wear and tear. Perhaps only opening if you have a sufficient cryptocurrency balance.
The bricks in your house all understanding their relative position to each other - and able to forewarn of subsidence.
Smart heaters which use thermal imaging to determine if you're cold enough to warrant heating up.
Not all of these ideas are sensible. Few are desirable. I doubt many are profitable. But the cheapness and ubiquity of modern chips means that they are all inevitable!