If you are using the Android iBeacon Library, no minSDK is required, and you can safely call most methods even on devices before Android 4.3, although doing so on older operating systems will do nothing but put a warning in LogCat. See here: http://developer.radiusnetworks.com/ibeacon/android/backward-compatibility.html
For this to work, just be sure you are using the Android iBeacon Library version 0.7.6 or higher or the Pro version Android Proximity Library 1.1.2 or higher.
Generally you will want to check capabilities in code so you can appropriately message the user or make alternate functional arrangements using code like below. But the API does not require that you do this.
public String getIncompatibilityReason(Context context) {
if (android.os.Build.VERSION.SDK_INT < 18) {
return "requires Android 4.3";
}
if (!context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE)) {
return "requires Bluetooth LE";
}
return null;
}