Bluetooth is a secure Wireless serial transmission protocol. There are bluetooth modules that behave like a serial cable between two points, or for an endpoint you can point a smartphone at to control a robot.

A number of robot controller systems incorporate this, for example more recent Raspberry Pi devices and esp-32 variants. Where not, there are add on chips/drop in systems to do this. For robots, off the shelf bluetooth chips, like the HC-06, are available and can be interfaced with microcontrollers. Keep in mind the relatively short range of such systems.

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It can use a Serial Data Stream system and has a range of up to a few meters.