Website detects if a phone is using Wi-Fi or Cell service

I have some videos on our page, and am curious if there is anyway for the website, or something on the back-end to detect if the user is connected to the site either through Wi-Fi, or through their cellular network? I know Google Play can detect it, because I've seen it pop up messages saying the update I'm about to download is considered "large" and I should connect to Wi-Fi before I try to download it. This warning pops up only when I have Wi-Fi turned off.

Is there a way to have the website be able to detect how the user is connected (Wi-Fi or cell network), and pop up a warning to the user when they try to play a video if they are on a cell connection?