Been there. Had a cheapo tester show me hot on a dead line and I touched it, luckily just got a tingle. After that nonsense I grabbed a Fluke and never looked back. The real trick is to test it on a known live circuit before AND after you check the suspect wire, every single time. Those $12 ones will pass the first test then crap out on the second when the battery starts dying. Klein makes decent stuff but the habit matters more than the brand.