How does a remote control work, and what is HDMI-CEC?
Most remotes send pulses of infrared light — invisible flashes encoding a number — and the newer ones use radio instead, which is why some need pointing and others do not.
Infrared remotes. An LED emits infrared at around 940 nanometres, flashed on and off in a pattern. To avoid being swamped by sunlight and room lighting, the signal is modulated onto a carrier, typically around 38kHz, and the receiver filters for exactly that flicker rate. The pattern encodes a device address and a command code. This is why you must point it, why it bounces off walls and sometimes works indirectly, and why it fails through furniture.
You can see it. Most phone front cameras lack an infrared filter, so pointing a remote at one and pressing a button shows a flashing light — the fastest way to test whether a remote is transmitting before replacing batteries.
Radio remotes, using Bluetooth or a proprietary protocol, work through cabinets and around corners, support voice input and two-way communication, and must be paired rather than simply working — which is why a replacement is not a straight swap.
What HDMI-CEC does. Consumer Electronics Control is a low-speed control channel carried on a dedicated wire inside every HDMI cable. It lets connected devices command each other: pressing play on a player turns the TV on, switches to the right input and sets the volume, and one remote can control several devices without any infrared at all.
Why it is confusing. Every manufacturer brands it differently — Anynet+, Bravia Sync, Simplink, Viera Link, EasyLink and others — so it is frequently not obvious that they are the same feature and interoperable.
Why people turn it off. It causes unwanted behaviour: a device waking the TV unprompted, inputs switching by themselves, or a soundbar seizing volume control. Disabling it on one device usually resolves it.
Universal remotes work by holding a library of infrared codes; learning remotes capture them from the original.