This is a Raspberry Pi 4. It can control many things, through Bluetooth, WiFi, RF, Infrared and many other clever protocols.
It can interface with wires and relays and LEDs and buzzers and.. the list goes on..
It also uses very little power and, most importantly, runs SILENTLY.
It is cheap, reliable, and very small.
This is the Core of my Home Automation system and interfaces to several of these little beauties:
I have discreet devices that are easiest to control directly with a microcomputer such as the Raspberry Pi Zero W.
The "W" stands for Wireless" which means it is possible to plug just a USB power connector into a Zero W and have it run "headless" but with the ability to log in to it remotely with a full graphical interface for maintenance.
The Zero W has all the same connectivity as a full Pi 4, but is even smaller. Here's one of mine next to a 50p piece.
The storage is provided by a micro-SD card (sticking out the left side).
They cost £9.80 and the SD card costs £6.49. A decent power supply costs £8.
The software is free, so for less than £25 you have a hugely sophisticated Home Automation add-on device that can control virtually anything.
I use my "satellite" Pi's to control or provide: