microcontroller for connected bracelet

Hello,

Currently I am working on a project that consists of the realization of a connected bracelet. This bracelet itself will have a single function that will alert the user when his phone is disconnected from the bracelet. So the bracelet will prevent phone losses. To be more precise, the bracelet must be permanently connected with the phone and when the connection is broken, the bracelet must alert the user. So I'm not trying to insert all the latest features of the connected bracelets.

At the moment, I managed to make a prototype thanks to an Arduino uno and a Bluetooth module. The problem is that the Arduino takes too much space so I would like to use a microcontroller suitable for bracelets.

But I have no knowledge of other types of microcontrollers that may exist. So I ask your help to tell me the types of microcontroller that I should use and also how to program them. I also ask you to tell me if there are Bluetooth modules suitable for bracelets. I also ask you to try to detail everything because I have absolutely no knowledge about the microcontroller that can exist or how to connect them or how to connect them to the computer or how to program them. So I assure you that all I know is the Arduino. So I seek your help because I am completely lost for months and despite my research on the internet I feel no longer advanced in my project. Please, I need help.
And also if there is someone who knows how are made and assembled pieces of bracelets connected, I would love to know.

I thank you in advance

Thank you. I saw the video but I don't know which type on microcontroller the guy use. And also for the programming of the microcontroller.

That link has all the details- it uses an Arduino Pro Mini and a BlueSMiRF module for the bluetooth.

Thanks. But I think using an arduino and a separate bluetooth module will increase my bracelet. But I would like to have a bracelet of rather small size. So I wanted to know if there is not a small microcontroller that already contains bluetooth.

There's not an genuine Arduino one, but the ESP32 is fairly small, has inbuilt Bluetooth and can be programmed with the Arduino IDE.

Boards based on the Nordic Semiconductor nRF52840 chip are looking good. nRF = ARM CPU with integrated Bluetooth. Adafruit and SparkFun sell nRF52840 boards usable with the Arduino IDE.

Adafruit and SparkFun make Arduino compatible boards but these are not products of Arduino.cc. They are all separate companies that compete and co-operate at the same time. They have their own websites, support forums, etc.

Come to think of it, the Beetle BLE would probably be your best bet. It is very small and has onboard BLE.

thanks for all. I can continue the rest myself.