Joules capacity: Surge protectors can absorb a certain amount of this unit of energy before it is at capacity. The higher the surge protector’s Joules capacity, the better it protects your electrical system, appliances, and technology. Voltage protection rating (VPR): The VPR is the baseline voltage for what a surge protector will filter out. You’ll want to find a surge protector with a low VPR rating so that it kicks in earlier. Response time: Immediate diversion of unsafe voltage is vital for protecting your home. You’ll want to look for a surge protector with a nanosecond response time or even less.