I always thought you had to get the store-bought kind. Putting one together from old components got me out of a tight spot last week. Now I always carry one in my van.
Real understanding of a tool beats just owning one. Those store kits don't teach you how the circuit actually fails. Building your own means you can probably fix the real alarm too.
Yeah that bit about real understanding is so true lol. I fixed a buddy's motion sensor last month because building my own tester let me see how the signal decayed. Was just a bad ground connection but I never would have spotted that with a store-bought kit.