I want to monitor the cellular signal strength. My testing device use WCDMA.

telephonyManager.requestCellInfoUpdate(mainExecutor,object : TelephonyManager.CellInfoCallback() {
    override fun onCellInfo(allCellInfo: MutableList<CellInfo>) {
        allCellInfo.forEach {
            val s = (it as CellInfoWcdma).cellSignalStrength
            Log.d("requestCellInfoUpdate","ASU=${s.asuLevel}, dBm=${s.dbm}, level=${s.level}")
        }
    }
})

Gives requestCellInfoUpdate: ASU=96, dBm=-24, level=4

Looks fine, but I want to monitor the change. So I set up a PhoneStateListener (My device is Android 11, so no registerTelephonyCallback yet)

private val phoneStateListener : PhoneStateListener? = object: PhoneStateListener(){
    override fun onSignalStrengthsChanged(signalStrength: SignalStrength?) {
        super.onSignalStrengthsChanged(signalStrength)
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
            signalStrength?.cellSignalStrengths?.forEach {
                val s = it as CellSignalStrengthWcdma
                Log.d("onSignalStrengthsChanged","ASU=${s.asuLevel}, dBm=${s.dbm}, level=${s.level}")
            }
        }        
    }
}

telephonyManager.listen(phoneStateListener,PhoneStateListener.LISTEN_SIGNAL_STRENGTHS)

which gives me onSignalStrengthsChanged: ASU=55, dBm=-65, level=4 instead

It seems that the value obtained by PhoneStateListener.LISTEN_SIGNAL_STRENGTHS is wrong, is it? Do I have to call requestCellInfoUpdate within onSignalStrengthsChanged to get the true signal strength?

It also seems that the ASU level get by requestCellInfoUpdate never update. If I put the phone in a microwave,

requestCellInfoUpdate gives ASU=96, dBm=-24, level=1 while

onSignalStrengthsChanged gives ASU=23, dBm=-97, level=2.

I have no idea which value is right.