Device showing signal Strength if no Sim is present

Question

I have used the following code to get the signal strength,

    SignalStrengthListener signalStrengthListener;
    signalStrengthListener = new SignalStrengthListener();
    ((TelephonyManager) getSystemService(TELEPHONY_SERVICE)).listen(
            signalStrengthListener,
            SignalStrengthListener.LISTEN_SIGNAL_STRENGTHS);

and then it is listening for the Signal strength,

private class SignalStrengthListener extends PhoneStateListener {
    @Override
    public void onSignalStrengthsChanged(
            android.telephony.SignalStrength signalStrength) {

        // get the signal strength (a value between 0 and 31)
        int strengthAmplitude = signalStrength.getGsmSignalStrength();

        // do something with it (in this case we update a text view)
        // signalStrengthText.setText(String.valueOf(strengthAmplitude));
        if (strengthAmplitude > 30) {
            signalStrengthText.setText("Good");
            // signalStrengthText.setTextColor(getResources().getColor(R.color.good));
        } else if (strengthAmplitude > 20 && strengthAmplitude < 30) {
            signalStrengthText.setText("Average");
            // signalStrengthText.setTextColor(getResources().getColor(R.color.average));
        } else if (strengthAmplitude < 20) {
            signalStrengthText.setText("Weak");
            // signalStrengthText.setTextColor(getResources().getColor(R.color.weak));
        }

        super.onSignalStrengthsChanged(signalStrength);
    }
}

It works good if the sim is present in the device. But when I remove the sim from the device and then check for the signal strength, it still provides some value for the signal strength.

One possible solution, I can think of is to first check, if the sim is present in the device or not and then show the signal strength. But I would like to know an explanation for this weird behaviour and a possible solution for it.

Answer 1

no USIM is required for cell service - only for authentication. else emergency calls would fail.

it's not weird at all... that is common sense, since you do not remove the radio nor disable it.

a simple test: remove the USIM, call emergency services, pretend you were pocket dialing.