Develop Reference

Connecting to bluetooth device with a best rssi

I want my android device to pick a BT device in range with a best RSSI and connect to it. Is there a way to implement such thing?
Ex: I have 5 ESP32-based devices around my house and need my phone to reconnect to the closest device (with a strongest RSSI). Is there a way to make app automatically pick the best RSSI from the available list of devices, terminate previous connection and reconnect to the device with best RSSI?
Your help is greatly appreciated. Thanks.

Yes this is definitely doable. All your app needs to do is the following:-
Scan for devices for a specific interval (e.g. 5 seconds).
Filter the scanned devices based on their name (i.e. you want to make sure that you only have the ESP32 devices and not other random Bluetooth devices).
Find the device with the best RSSI.
Connect to the device with the best RSSI.
If you want the process to be continuous, then go back to step 1.
However, keep in mind that RSSI does not always equate to distance/range. The device with the best RSSI might actually be further than other devices. The links below go over this plus some other useful data that you might need for your application:-
The ultimate guide to Android Bluetooth Low Energy
Using BLE for indoor positioning
Bluetooth LE RSSI for proximity detection

Bluetooth device data transfer issues

How can a device identify the other devices to whom we need to send data and transfer the data to other device.
If the device1 send the data to device2, will other device say device3 near to them will receive same data?

Please read up on the whole Bluetooth story. You seem to have problems with basic concepts. Also, it would probably help to be a bit more specific in your questions for example specifying which BT version are you referring to.
For identifying the devices, each of them has a separate address. They even have human readable names. (Look at the Wiki page linked above Connection and communication) Also, during the pairing process, you should have to get to know and explicitly allow the devices which you really want to communicate with, the goal of the process is exactly to make sure to have an explicit authorization between the devices for communication.
Yes, device3 will receive the radio signals, but if not authorized, it won't be able to tell what is going on - unless it is a misbehaving device cracking the encryption... (Given the communication is actually encrypted, that is.) Reading the Security Concerns part is also useful.

Bluetooth can connect up to eight devices simultaneously. With all of those devices in the same 10-meter (32-foot) radius, you might think they'd interfere with one another, but it's unlikely. Bluetooth uses a technique called spread-spectrum frequency hopping that makes it rare for more than one device to be transmitting on the same frequency at the same time. In this technique, a device will use 79 individual, randomly chosen frequencies within a designated range, changing from one to another on a regular basis. In the case of Bluetooth, the transmitters change frequencies 1,600 times every second, meaning that more devices can make full use of a limited slice of the radio spectrum. Since every Bluetooth transmitter uses spread-spectrum transmitting automatically, it’s unlikely that two transmitters will be on the same frequency at the same time. This same technique minimizes the risk that portable phones or baby monitors will disrupt Bluetooth devices, since any interference on a particular frequency will last only a tiny fraction of a second.
So what if they interfere and there is a erroneous data, the receiving system simply discards it based on correcting bits of the packets transffered.
Bluetooth devices have a parameter or option called visibility. When you enable visibility, then the bluetooth device starts
publishing its presence within the bluetooth frequency range. This presence can then be detected by any other bluetooth device which can connect to this device when
it scans the above bluetooth frequency range.
As they use spread-spectrum frequency hopping described above they
publish data to all receivers but only the intended receiver with whom
the sender is connected will have the key to unlock the data.

Read power input from usb

Is there any way to read the power input from a USB connection in Android?
For example plug in a micro usb lead into the phone from either a computer USB output, a mains charger, or something similar and read the voltage and amp output?
I have no idea where to start looking for this information, and when searching I can only find battery widgets, or power consumption apps - this is not what I'm looking for, I want to be able to read how much power is being sent via the USB interface that is connected.
Many thanks.

Probably, You should start with BatteryManager , refer to this question for some examples of usage. I believe the data provided by BatteryManager should be enough to provide approximate calculation of what You want to (how much power is being sent via the USB). Having device id and table of devices default batteries capacities or/and users input about capacity and % difference with time interval and voltage probably would give enough info for approximate calculation of consumption
Another (dirty) way might be the following - dig android sources if ones have any info about total capacity / consumption You can obtain e.g. with java reflection. I think BatteryManager and BatteryStatsImpl could be appropriate places to start analysis from.

Android - When scanning for bluetooth devices, is my device discoverable?

Quick question,
As the title says -
Is my device discoverable when it is searching for other discoverable devices?
Thanks

No it is not - The radio can do only one thing at a time at the very lowest level. When scanning the process is continuous utilizing all the slots and nothing is available to perform any parallel activity

Unless you check the box to be discoverable(See your Bluetooth settings) your device will remain stealth during the search .

I don't think so.
Searching doesn't require broadcasting, only receiving the beacon signals of other broadcasting devices.
Think of it like looking for WiFi. You can see the hotspots because they want you to, but you aren't really broadcasting your information in the process.

Android App Bluetooth Determining distance between paired devices

so I'm trying my hand at android developing this summer. I was trying to make a sort of alarm app when a pair of connected devices go out of range of each other.
From looking around on the internet / stack overflow, it seems that looking at the RSSI value will help me achieve this.
However, it seems that the RSSI value can only be read at the time of connection with the device, that is it doesn't update itself (or there is no method to do so).
Is the RSSI value the only way to achieve my goal?
Would it be possible to use RemoteDevice and RemoteDeviceHelper? Has anyone tried this?
Any other suggestions and hints would be much appreciated

You could establish a connection with the device and exchange heartbeat information with the device , you can use the reception of valid heartbeat information to detect device being in range and or going out of range..
Your algorithm can use this information in conjunction with the connection loss to detect device being out of range and set off the alarm.
RSSI in Android available via public APIs is only during the discovery process, the other non public means of reading the RSSI (like in RemoteDeviceHelper) should also be possible , but RSSI by itself is not a good indication of distance.