When/ how can you tell if your child understands no? DS is crawling and into everything. His favorite place to head is the outlets that have plugs in them. I have told him no repeatedly and redirected him but he goes right for it again. DH said the same thing was happening with him. I gave him a little swat on the hand and he laughed at me!!!! I think he thought I was trying to play pattycake with him...I had to try really hard not to laugh back!!!
Anyway, I am not sure if he understands the word no and if I am spanking him too young. He definitly knows his name so does he know No??
Any insights would be so appreciated!!!

I think that understanding NO and actually not doing what you've been told NO to are different things...I think kids understand it a lot sooner than they obey it. We started swatting our fisrt son's hands as soon as he began reach for things we did not want him to get into. As long as you are consistent in what you are redirecting him in, it will eventually sink and and he will respond appropriately.

Yeah i agree with Chellefish.

ok, so I am not a practicing mom yet (baby in my belly) so my thought couild be competely stupid. but when I was reading your post I thought to myself what about as you are saying NO you clap real loud and/or stomp...something loud enough to scare or startle them. I don't know if a child would think that was a game too, but wouldn't they begin to associate NO with being somethning scary? Any thoughts on my idea would be appriciated since I am new at this whole *mom* thing.

He just doesn't make the connection yet. Be consistent. When he reaches for something off limits...smack/swat/flick the hand and sternly say "no! no touch" and I know, they often laugh and darn if that ain't the cutest little laugh and grin EVER..but you have to say it again...seriously, sternly..."No! No touch!" you can add in something like 'bad owie' if you'd like. And just AS SOON as he reaches again, you flick and say it AGAIN and remove/redirect. But try to catch the offense as soon as possible and ALWAYS react the same way "No, no touch" with a flick. Flick as you say no, that helps make the connection. no = pain
Be consistent. He'll catch on ;)

Eventually, he will reach for the outlet, you will say "NO" and he will hesitate or stop. Then you know he knows "NO". :D

Yea, consistency is key. Keep plugging on, he'll get it eventually! I used to think that kids understood EVERYthing (I treated mine like they were 40 year olds sometimes) but my DS says things sometimes that there is no way he knows even remotely what he is saying - he is only parroting what he heard somewhere else. That is how kids learn, but they need lots of repitition for it to stick!