Looking for “Onlog” in Google Play you will find applications that can notify you when someone connects to WhatsApp and is “Online” without the need for you to connect to the messaging app. These applications give a connection report of a contact. For example, knowing how many times they connect and at what time they disconnect per day.
With Onlog, everything consists of entering any name and phone number and then just pressing “start to follow”, the application will notify you when that contact connects and disconnects from WhatsApp in real time through a notification.
When entering the OnLog application you can see details of the connection and disconnection times. On the right you will see the time that you have connected and disconnected.
Sometimes applications of this type disappear from Google Play, but you can safely download others that are similar and have enough positive ratings and user downloads.