It started with me thinking of traps for a puzzle box. If one of my players missed a disable device check, a trap would spring and small needles would project out of the box and poke their hands. I was thinking that these needles (instead of being poisonous) could make the players hands go numb, giving them, maybe a minus 2 with things they do with their hands for a little while. I was thinking less than an hour. But I don't know if that makes sense? Is there something out there about numbing, or somewhat disabling body parts? Or if your whole body went numb? I mean, I'm just playing around with ideas and I'm pretty new to GMing so I won't be crushed if there isn't or it doesn't make sense. I thought it would be kind of cool/funny. I know my group would make the situation humorous, and there is a chance it wouldn't happen if they got the check. It would be a Fortitude save right? Thanks!
ps: I'm not quite sure if this is the right place for this question? Please correct me if I am wrong!
If you want it to exist, it exists.
There's no specific rule about numbing (other than full-body numbing, also known as paralysis), so you're free to do it on an ad-hoc basis. The -2 would probably be a pretty mild numb, more like your hands barely falling asleep.
A Fortitude save seems most appropriate, yes.
There are Called Shot rules that give some numbers to the downsides of painful injuries to particular body parts. Treating the needle trap as a called shot to the hand would work, perhaps as a Critical Called Shot on a failed save and a Called Shot on a successful save, with Debilitating Blow for them totally blowing the save.
The save most associated with traps is generally Reflex, and if anyone in your group has Trap Sense (which helps Reflex saves versus traps), they might feel your trap was bypassing their trap-specific defences with a Fortitude Save.
There are several things already that make fine hand movements (like lockpicking/trap-disabling) impossible so you could make it like that for 1/6*10 minutes with a fort save to negate or partially eliminate (for the -2). That would also add the clever gameplay mechanic of "now I have to carry this trapped box around to open later, how to I store it?"
To build on Idle Champions idea, maybe give him two saves, 1 reflex to dodge the trap, and a fort to reduce the numbing effect. All of this is of course up to you and should be decided based on your perception of the party's strengths and weaknesses.