Implementing a dual wielded item.

I'm adding custom sickles as a weapon and I was wondering how to go about implementing a dual wielding feature. I know of course I can't actually make the offhand deal damage but I was hoping there was some way to know if they player is holding a sickle in both their offhand and main hand and that allow attributes to be different as opposed to only holding one in either hand. My plan is to end up having it be where when you hold both sickles you deal damage faster and a slight damage increase.