Knockout Count is one of the simplest blackjack systems available and also one that I would recommend for beginners as a reasonably profitable yet simple card counting system. KO Count is an unbalanced, single level card counting system which means you won't end-up with zero at the end of the deck/shoe and there are only -1, 0 and +1 values in the counting system.
Here's how the Knockout system works:
|2, 3, 4, 5, 6, 7||+1|
|T, J, Q, K, A||-1|
You might notice that KO Count has a lot of similarities with the Hi-Lo Count. That's true; one of the two differences in the systems is that sevens are valued as +1 in the KO Count.
The Knockout card counting system is often advertised as one that'll make life easier for those who have trouble converting from running count to true count, which is the second slight change in the system compared to High/Low system: you don't convert running count into true count when counting according to the KO Count. When using the High/Low count you'll have to convert from running count to true count.
The expectation of the Knockout Count (and any counting system) depends on the amount of decks and the bet spread used. With a low amount of decks (1-2) and a wide bet spread (1-10) you can easily make profit by using a simple system like the KO counting system, although then the risk of getting caught is also much greater, because dealers and pit bosses recognize this card counting system.
To find a detailed explanation of Knockout Count, read Knock-Out Blackjack by Olaf Vacura and Ken Fuchs.