if something in the gym bag presses on the button, pop will of course go the top which it is of course designed to do, and the pop top with one hand is why I purchased this in the first place. One bout with a gym bag full of water has me being much more careful now to keep it locked when it's being banged around. Works GREAT. I love that I can add electrolyte powder or potassium powder (and yes, I add mineral salt to my water as well) and shake this bottle hard to mix everything up. My go-to gym water bottle. I dropped it once on the hard floor and no cracks. Happy. Overall great buy and I highly recommend