The below code works in simulator but not on device.
Tested myself on va3 with SW-Version 2.60 with CIQ 2.3.4, Eclipse 4.6.3 with CIQ 2.3.4
using Toybox.WatchUi as Ui;
using Toybox.Graphics as Gfx;
using Toybox.System as Sys;
using Toybox.Lang as Lang;
using Toybox.Application as App;
var lowPowerMode = true;
class TestWatchView extends Ui.WatchFace {
    function initialize() {
        WatchFace.initialize();
    }
    function onLayout(dc) {
        setLayout(Rez.Layouts.va3(dc));
    }
    function onShow() {
    }
    function onUpdate(dc) {
     var time = Sys.getClockTime();
     var field = findDrawableById("Label");
        field.setText(time.sec.toString());
     field = findDrawableById("Label2");
        field.setText(lowPowerMode.toString());
        View.onUpdate(dc);
    }
    function onHide() {
    }
    function onExitSleep() {
     lowPowerMode = false;
    }
    function onEnterSleep() {
     lowPowerMode = true;
     Ui.requestUpdate();
    }
}