Command blocks with /testfor still sending signals

I am working on a map called "Parkour PvP" until I got to a command block that has a /testfor command in it. The command block is still sending signals even when the command block is not being powered or the command being invalid. Command I used: /testfor @a[score_Deaths=5]. The comparator was still turned on when I removed the power or I make the command block have an invalid command. Something good for free redstone signals without levers, buttons, pressure plates, redstone blocks and redstone torches. I had a score of -1 and the command block still thought that I had a score of 5.