The activation window gives an immediate confirmation that the indicator is armed as it turns from yellow to green. If this doesn't happen immediately, then fully re-squeeze the button between thumb and finger. The breach/indication window (white with a red border) is separate so that you can clearly see if there has been a breach of the 10ºC/50ºF temperature threshold. If no breach has occurred the window will remain white. It will turn blue if there is a breach.