OnLog is an exclusive app for Android that allows you to know when someone connects to their own WhatsApp without even having to enter the messaging service.

Once you download the app and indicate the person or people you are interested in following, every time they enter WhatsApp, OnLog will send you a real-time notification. This app not only tells you when the user logged in, but also the time it was online and offers you a history of their records, even if the person has blocked you.

Note: OnLog has received some controversy and has been removed from the Apple store for 'undisclosed reasons'.