Bouv nailed it right here.
To answer the OP, most of these things have been invented. And many have even been distributed. But they were abandoned because they didn’t sell.
Not enough people wanted them, compared to other features or to a lower price. Some survive as special after-market devices that a few people buy, but most have been dropped.
My son has this in his bathroom. I think he also has a pressure regulator so that no matter what faucet (or washing machine, etc.) is being used, the ressure stays the same - and the temp, too, of course.
I keep an inverter in my truck. Basically, I plug that into one of my lighter sockets (I’ve got THREE!), and then I can plug one standard electrical device into the outlet on the end of the inverter. It’s useful. I can easily charge my cellphone, or run an air compressor, or charge batteries.
So why the heck don’t cars come installed with inverters? I shouldn’t have to spend an extra forty bucks or so just to be able to use standard electrical devices in my vehicle? Seriously, I need a standard outlet a LOT more often than I need a lighter outlet.
A DVD player that has all necessary #$%!ing controls on the unit itself.
Hey, I just rented a movie, but, uh-oh!, the DVD remote is dead! Maybe – just maybe – I’ll be able to actually watch the movie; I can hit “Play” a lot and hope that “Play Movie” is the default option on the main menu. If it isn’t, I guess I’ll have to get my kicks by selecting the English audio track 2,531 times. Even if it is, though, I hope I didn’t want to watch any of the special features, or use subtitles, or adjust the volume without messing with the stereo, or…
I have an inverter for my car, too. I bought it so my son can play his GameBoy on long trips. Yeah, an inverter-type plug would be a lot more useful than the lighter-type plugs.
There are several things that already exist, but which I wish were cheaper/smaller:
-Air conditioning/cooling. Air conditioners and refrigerators are huge and heavy and expensive and full of dangerous substances and copper tubing and stuff. Someone should invent a much smaller and faster cooling method.
-“3d printers”. Devices exist that make 3d colored wax sculptures of computerized data, but they’re INCREDIBLY expensive. They should be cheap. For that matter, mass-producing multi-colored 3d models should be cheap. Wouldn’t it be cool if every board game you brought, instead of coming with little single-colored plastic shapes, came with tiny but perfectly colored and shaped little models?
-3D VR goggles need to be VASTLY improved still
-a “cooking machine”. It would be about the size of a large oven, and it would be to fresh-cooked food items in general what a bread machine is to fresh cooked bread.
The problem I see with that is that people will then plug all kinds of nonsense into their car, drawing more power than the inverter was designed to deliver, and blowing a fuse. I know, not a calamity, but it could be for the mechanically-disinclined, and they’d blame the carmaker for not warning them that they couldn’t plug their Alienware PC, their blender, and their vacuum cleaner into their little Volkswagen at the same time.
Here’s my invention idea. You may not steal it, because I plan to try to make one someday. So, no stealing, you stealers! Okay, here it is: an alarm clock with a keypad on top and a random number generator inside. At the set alarm time, the clock will go off, and will display a random three-digit number on the clock display. The alarm will not be silenced until the code is punched in. This system ensures that a person must be awake, open-eyed, and coordinated enough to enter the code. No more snooze bar, no more half-asleep alarm turn-offs.
1.One-month wipe-on insect repellent for humans–along the lines of the flea stuff you put on dogs and cats.
2.Uniform controls for headlights, wipers, etc. Every time I drive a borrowed/rented Asian car–Japanese or Korean-- at night in light, variable rain I inadvertently shut off the lights because the light switch is located in the same spot as the wiper controls on my American vehicles.
And because the wipers are where I expect to see the automatic transmission lever, I turn them on while looking backwards and gunning the engine expecting to reverse.
Great idea!
I’m one of those people who usually has to push snooze a couple (ok, five) times before I get up. I have a very nice alarm clock that plays CDs, so I can alternate my waking-up soundtrack every week or two. Unfortunately the snooze button is tiny teeny and right beside the off button. What freakin’ idiot designed that?
I also have this travel alarm which I love because the only button you can push on its surface is the snooze button. All of the other buttons to set the alarm are underneath a cover that has to be removed (pops off very easily). This way I can’t accidentally turn off the alarm.
I haven’t yet been able to find a real alarm clock that plays CDs, where the only easily accessible button is the snooze.
Or you could just put your alarm clock across the room, so you have to actually get up and turn it off. 
I would just sleep through it. The only reason I turn off my current alarm clock is because my husband hates it. I haven’t found an alarm yet that is obnoxious enough for me to want to turn off.
Right now, I have two alarm clocks–an electric clock radio that turns the radio on about 45 minutes before I intend to get up, and a battery-powered beeping alarm clock. The battery-powered clock has been a blessing on numerous occasions, when the power when out at night, and the back-up battery in the electric clock didn’t work long enough. It also has only one button to push–the snooze button. All the other settings require more effort to use, so I can’t accidentally turn it off when I hit snooze. It’s similar to Waenara’s, but also different.
I can’t agree with you more!!! While I do like remote controls, I really don’t see any logic at all behind putting the most important functions on a device that is not attached to the player. However, they’ve been doing that since the days of VCRs, where you had to use the remote to set the clock, or program the recorder. If they want to force us to depend on the remote, then they should put in the remote finder someone else suggested. I would bet that most people would be willing to pay a little extra for it until it became standard.
Not to be a negative nancy, but…umm…we’re kinda limited by the laws of physics on this one. We actually DO have things much smaller and practically no toxic chemicals at all, they are called thermoelectric coolers. Basically, you put two certain types of metals next to each other, crank up the voltage between them, and one side ets hot while the other gets cold.
As to why we don’t use big large ones in our windows instead of current AC units, I don’t know. I’m not knowlegable enough on the subject to say if it can be used on a large scale practically or not. But my guess, since it hasn’t been done, is that it cannot be used on a large scale practically.
Yes and no. The laws of physics certainly say that it will take a certain amount of energy to do a certain amount of cooling. But I’m not sure what they say about size and weight.
You didn’t ask for recommendations, but I’ll give you the same one that I gave Audrey Levins anyway: try the Sonic Boom (it’s only $40). I am a notorious alarm-sleeper-through-er, and I was a little skeptical of this alarm clock before I tried it, but when both the tone and volume are turned up it’s like a damn air raid siren. 
If I’m understanding correctly, the Toyota Sienna has this.
That’s what I’m doing since I’ve moved into my new flat, and it works very well ! 
and
a) it’s inefficient compared to condensor style refridgeration.
b) you need to figure out someway to cool the hot side otherwise the hot side will just heat up the cool side.
c) it’s expensive to make.
You get a remote control, plus a bunch of bulky, inconvenient key fob locators that can’t be easily attached to the devices you’re likely to misplace - the funny thing is that this is a great example of truth in advertising; the product photo clearly demonstrates that the locators are bulky and inconvenient and that you can’t easily attach them your devices.
Pacifiers with voice-activated locators. I would’ve killed for one of these when my son was hooked on the binky. He simply COULD NOT go to sleep without one for a long time. Constantly hunting for it was a drain on the nerves and I was pregnant with my third child to boot (my son was less than two years old at the time). I kept several extra binkies in the house, but sooner or later, they would all hide from me at the same time!
It already exists I think. In a few cars.
But I want more car companys to come out with heated stearing wheels. I hate wearing gloves to drive.
When it’s -20 f, that would be a real, real nice feature.