Exercise bike that makes you exercise
Everybody knows one of the big problems with exercise machines is they end up as clothesracks. I've seen this literally happen. A lot of people put their machine in front of the TV to make them use it, for a while we even had no couch.
Here's an invention to create an exercise machine you'll really use, if you watch TV. The machine, or a device attached to it, would be programmed to constantly broadcast a recorded infrared signal trained from your remote. This code would be one that would interfere with watching TV. For example, volume-mute or channel-up, or a digit. Whatever you want to train it to. (Off doesn't work as that also turns the TV on.)
However, once you get on the machine and start using it, it stops sending this code, and you can watch TV. Once you have done your exercise quota, it would stop sending the muck-up code until you are next due to exercise, whatever your schedule is.
To stop you from just covering the transmitter with clothing (remember the clothesrack?) it would also need to have a receiver some distance away which gets upset and chirps annoyingly if it can't see the regular ping from the transmitter.
Others in the house not on a regimen could enter a code on the remote to temporarily disable the system when they want to watch. If 2 or more people had a regimen, they would have to enter which person they were to activate their disabling code. That gets a bit messy but it can be done.
And to stop people from just ripping the thing out, which they could always do, it would also have a remote control sequence that turns it off but "costs" the user more exercise later. Of course, if you use it all the time, you will eventually abandon the system -- some discipline is needed, but less than ordinary machines require.
So many machines go unused that something like this seems like the right plan.