How can you tell if someone is using WhatsApp Web?
To know if your WhatsApp web is active on an unknown device, go to the three dots given at the top right corner of your WhatsApp window. Go to WhatsApp Web and check the list of all open sessions. This will let you see all the devices that are connected to your WhatsApp.
Does WhatsApp Web Stay logged in?
How long does WhatsApp Web stay connected? You will be automatically logged out of WhatsApp Web after 30 minutes of inactivity. When you sign into WhatsApp Web, you can check a box under the QR code which says keep me signed in. Then you will stay connected as long as WhatsApp is connected on your phone.