2edgesword, it's better to have them and possibly have the time to employ them, than not have them and have no option to do so regardless of heads-up time. At least, I think so.
As noted earlier, I have a three-alarm system:
If noise in general isn't enough deterrent, the 50lb and 60lb dogs are both big enough to do damage, and have very attention-getting barks (deep and loud). In any case, they bark if anything happens near the house. That should normally be good for at least several seconds heads-up time, and usually more like 30 seconds or more (based on delivery guys, visitors, etc).