For power moitoring, I recommend this app - it's designed for that, and it works well.
I'm not well-qualified to explain the intentions of Device Activity Check (DAC), but I'll give my $0.02 here...
I find DAC super useful for big-picture device health -- IMO, it does an great job of balancing being a simple & lightweight app that still has wide reach for alerting me to an unresponsive device in a reasonably timely manner (e.g. battery dies in one of my rarely-used window sensors - I'd otherwise potentially not notice that for months since my window sensors have wonky battery reporting, but they do routinely report a temperature [so no temp-report activity w/in 24 hrs = dead battery in that case]).
If you need immediate (or very specific) status alerts, DAC isn't intended for that -- there are other options (such as the app I linked above) that can better handle unique/specific needs.
