How to calculate distance between two Bluetooth devices?

Yes, it is possible to do at some points, definitely, it has some limitations.

You are using Cordova, I am assuming your requirement is for Android and iOS devices.

In Bluetooth devices, the RSSI value will bring you approximated but with a high accuracy distance, it works up to 9-12 Feet.

There is one formula to convert RSSI values in the feet or meters, Bluetooth plugins for Cordova are also providing hooks where you can add some alert or beep logic.

Distance = 10 ^ ((Measured Power -RSSI)/(10 * N))

Where 

• BLE uses Measured Power is also known as the 1 Meter RSSI. So consider the value of Measured Power = -69
• RSSI = Obtained RSSI value from the devices (For example, you obtained -80)
• N = 2 (Consider Low strength)

Put the values into the above formula to calculate the distance:

Distance for RSSI -80 = 10 ^ ((-69 -(-80))/(10 * 2)) = 3.54 meters

Distance for RSSI -75 = 10 ^ ((-69 -(-75))/(10 * 2)) = 1.995 meters ≅ 2 meters

While the covid pandemic time I made some research on it and I was working on an application to manage a safe 1.5 Meter distance.

You can find the project made using Vue js and Cordova plugins. 

Github

Convert RSSI values to Meters Formula

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Limitations:

1. For iPhone, security matters the most. You can keep Bluetooth on until you are accessing the phone, after a few minutes it will kill the process on its own.
2. Wearable Devices might be found, might not. Because of the used middleware in the watches, it may ask to connect first - otherwise, it may/or may not give the permissions.

Sources: GITHUB & Medium