Wireless remote triggers are one of the essential camera accessories to keep in your camera bag. The theory is the remote trigger sends out infrared light, the camera's infrared receiver detects it and signals the camera to open the shutter.
IR detectors/receivers are little microchips with a photocell that are tuned to listen to infrared light. They are used for remote control detection –all TV, DVD player, and many digital cameras have one of these in the front to listen for the IR signal from the clicker. A matching IR LED inside emits IR pulses to tell the camera to release the shutter.
Digital cameras can have one or two infrared receivers/detectors built into the front or back of the camera body. You can find out in the camera’s manual. The IR receiver usually hides in the front of the right handgrip (top or middle).
Sony A7R II, A6300, NEX-5T all have one oval, infrared remote receiver hidden in the trim at the top of the handgrip.
Some cameras such as Nikon D3300 have IR receivers on both the front side and the back side of the camera.
One of the receivers that pick up the infrared signal from the optional ML-L3 wireless remote control is on the back beside the viewfinder. The other receiver is on the front-right side of the camera, near the middle of the hand grip. That is why you can trigger it from the front as well as from the back.