Most standard remote controls send signals to your home theater gear using a beam of infrared light, which a sensor on your hardware picks up. You can't see this beam, but your smartphone's camera can! So, if your remote isn't working right, you can use your phone to check if your remote needs fresh batteries.
Wake your smartphone and pop open its Camera app. Next, switch to the front-facing camera, point the remote at the camera, and press any button on the remote.
If the remote is working properly, you should see a flicker of light come from the IR blaster as viewed through your phone's screen that looks something that this:
If you don't see the flicker from the IR blaster, or perhaps just a very, very dim flicker, you probably need to change the remote's batteries. (And if new batteries don't help, you probably need to replace your remote. Sorry.)
Of course, this trick isn't limited to your smartphone's camera; many digital cameras can see infrared light, despite having filters to tune it out. So if all you have at your disposal is your laptop's built-in webcam, you may have everything you need.