WhatEye

WhatEye is an interesting app that lets you see when your contacts connect to WhatsApp.

Using WhatEye is surprisingly simple. All you need to do is enter the phone number for any contact you want to check on, then let the app do the rest. You can set up notifications for each time they connect or disconnect to the app. There's also a history section where you can see all the times they connected to the app in chronological order.

One of the most interesting things about WhatEye is that even if the other person has 'last seen' disabled, you can still see when they connect and disconnect thanks to this app and its continuous surveillance.

By comparing the connection times for two phone numbers, for example, you can determine whether those people were in a conversation together, which is an especially interesting function for anyone who likes playing detective.

The free version of WhatEye comes with 12 hours of free service, after which you'll have to pay to continue monitoring when certain phone numbers connect to WhatsApp.