# How doesn't signal amplification by means of antenna defy the laws of thermal dynamics?

According to this video you can amplify a signal by using the water in your head (although you could do the same thing with an antenna.) Does holding the key close to your head somehow drain the battery faster? Otherwise, wouldn't there be free energy contained in the amplified signal? How does that work?

• I don't know if that really works, but if it does, it's not "amplifying" the signal; it would be concentrating the signal, the way a lens can concentrate a light beam into a given direction. The signal's power is reduced in some directions and increased in other directions, but overall the power is not increased. Commented Dec 31, 2018 at 5:00

In a dark cave with a lit lamp in the middle light shines equally in all directions. If you put a reflecting mirror behind the lamp, the light will acquire a direction forward, turning part of the energy going back to the forward direction.

These electronic keys have no direction, there is no arrow to tell you how to point it. It means that the energy of the battery is distributed spherically from the key, the energy falling like $$1/r^2$$, and the part of the light/electromagneticwave that overlaps with the car's electronics , if carrying enough of the battery energy (close enough), will unlock/lock the car.

The water the gentleman holds acts as a type of mirror/reflector, actually as independent radiator, adding the spherically distributed energy from the key towards the car direction, as a second large source. Without it that energy would just dissipate in the distance.

Perhaps a simple way of looking at this is to compare it with a sound box on a stringed instrument whose purpose is to excite a larger number of air molecules adjacent to the sound box and so produce a louder sound than a string could produce by itself.

Look at the demonstrations starting at about $$4:26$$ in this video and note how the sound that you hear from a tuning is louder when it touches a hard surface.
In this case what is happening is that the tuning fork in both cases had the same amount of energy but more of that energy was used to produce sound waves in the air.
Energy was not being created rather more energy was being converted into sound waves.

As is stated in the video causing more (water) molecules to vibrate (equivalent to causing more hard surface molecules to vibrate) produces a greater intensity of electromagnetic waves from the the generator within the key fob.