Do you want to creepily spy on your friends, family and loved ones? Then Chatwatch is the app for you. It was previously removed from the Google Play Store as it allows you to spy on other WhatsApp users without their knowledge. Chatwatch now has a web version.
The app allows you to gauge when other users will be online, when they are most likely to be sleeping and more. All of this is possible because of the data that users allow Facebook to access. Whilst this data is not 100% accurate, it uses AI to create a best estimate. It also uses the information from WhatsApp's "Last Seen" feature - even for users have disabled.
You can test out the free 1 day trial on their website, afterwards you will have to pay $2 per week to track a pair of friends. It can be used to monitor up to 10 people at a time.