Would you keep a barbell loaded with the weight of your deadlift max in the glove compartment of your car?
Of course not, because even if that loaded barbell fit in your glove compartment, you would never try pulling that weight while driving. So why do people still talk about keeping grippers in the glove compartments of their cars and training them while at traffic lights? Because it seems clever!
It doesn’t work though.
Training to improve your gripper closing strength takes more focus and intention than what you can give while sitting in a car. Actually, when was the last time you’ve seen someone close a very difficult gripper while sitting? I never have. I couldn’t imagine closing my maximum without getting in a power stance.
Not to mention you should always chalk up while training grippers. Do you keep chalk in the glove compartment of your car? It helps to enhance your gripping of the steering wheel! What are you waiting for?! Just kidding you don’t need chalk for your steering wheel, that’s silly. 
That’s as silly as not chalking up for a max deadlift; you always want to chalk up on a heavy lift. Same with closing heavy grippers! If you aren’t chalking up for your training sets on our Genie Grippers, that’s a sign you’re half-assing your reps, and half-assed reps do nothing.
Another sign of half-assing is assuming you can train grippers without a warm-up. Just because the risk of injury is low when closing grippers, that doesn’t mean you shouldn’t spend a few minutes warming up for the effort. Start with a lower level gripper and pump it a few times. Stretch your fingers. Rest a few minutes. Repeat. Warm up your shoulder too. Hell, I even warm up my thoracic spine and get my glutes firing before I approach my gripper training sets. I like to really “come down” with force on the gripper, and that uses everything to my core.
The Genie Grippers are fun to play with, and you should play with them, go ahead! Just don’t expect to get to the next level without training them with the same preparation and intention you would use for bigger exercises like squats and deadlifts.