WatchOn is the Android App which is Universal Remote Control. It can be used as remote for TV, Set-top Box, DVD Player, Blu-ray Player, AV Receiver and Streaming Media player.

You have to point S4 towards TV or device which you want to control. This way you can switch on or off any device. Also you can browse all other options of device this way.

But if you want to switch off the TV when you are not pointing S4 directly towards it then it will not work. You can still switch off the TV using simple method. The main technology used in Galaxy S4 is infrared (IR) light (IR Blaster). The signal between Galaxy S4 and the device it controls (TV) consists of pulses of infrared light, which is invisible to the human eye. If you point Galaxy S4 toward the wall, the TV will not receive the IR light and it will not switch on or off.

You can achieve this by using a mirror. Place a mirror such that TV is visible through it. Then point the S4 towards the mirror. The IR light will get reflected towards TV which in turn will switch it on or off. If you have dressing table or big mirror in your room placed then you can use it to reflect the signal to operate the TV.