Here's a little trick that will save you some major headaches. When you curl up on the couch to watch your favorite show, the last thing you want is a remote control with dead batteries. But don’t get up just yet. Use your smartphone to see if you actually need to replace them.
Your smartphone can help you determine whether your remote control is faulty or whether the battery is dead, according to www.maketecheasier.com.

Here is how to go about it:
Pull out your smartphone and launch its camera app. Next, tap to switch to the selfie (front-facing) camera. Now, point your remote control at the front-facing camera. Then press and hold a button, any button on the remote, while pointing it towards the camera.
If your remote control is functioning properly, you should see a flickering light originating from the remote’s Infrared Radiation (IR) blaster. IR is electromagnetic radiation (EMR) with longer wavelengths than those of visible light, and is therefore generally invisible to the human eye (although IR at wavelengths up to 1050nm from specially pulsed lasers can be seen by humans under certain conditions. It is sometimes called infrared light. IR wavelengths extend from the nominal red edge of the visible spectrum at 700nanometers (frequency 430 THz), to one millimeter (300 GHz).
Most of the thermal radiation emitted by objects near room temperature is infrared. Like all EMR, IR carries radiant energy, and behaves both like a wave and like its quantum particle, the photon.

IR is emitted or absorbed by molecules when they change their rotational-vibrational movements.
If you don’t see a flickering light or the light is very faint, it means you probably need to replace your remote control’s batteries. And if even after replacing the batteries with new ones, the flicker of light does not appear, then your remote is the problem, in which case you might want to consider replacing it.
This trick does not only work with smartphone cameras. It can also work with any other digital camera out there. So, if all you have is a laptop, try using the built-in webcam, and it should do the trick.

Note: Not all smartphone cameras will work. Some camera apps have built-in technologies that might bar this trick from working. So, before you conclude that your remote is faulty, it is wise to try using a different smartphone camera to see whether you will get the same result.

Why it works
A standard remote control typically sends signals to your home theatre or TV using a beam of infrared light. This beam gets picked up by a sensor in your home theatre or TV. The thing about infrared light is that just like ultraviolet light, it lies outside of the colour spectrum that is visible to the naked eye.
Once the remote emits flashes of infrared impulses to the TV sensor, the sensor interprets by telling your TV which channel it should tune to.
A smartphone’s camera has a lens that acts more or less like the TV sensor when a beam of infrared rays is projected towards it. Unlike the human eye that is unable to see these rays, your smartphone camera can detect these infrared rays easily, and that’s why a flickering light appears on the smartphone’s camera.