WhatsApp popup notifications,Although it's not technically a lock screen widget, one simple thing to do on any device is go into WhatsApp settings > Notifications and enable Popup notifications. You can limit popups so that they only occur when you're using your phone or when your screen is switched off, or chose the option to always show popups.
If you go for the 'screen off' option, a new message notification will pop up even if the screen is off and remain on your lock screen until the next time you go to unlock your phone, as you can see below.
WhatsApp widget on stock Android
If your device is running Android 4.2-4.4 KitKat or a custom ROM that supports lock screen widgets, you can quickly and easily add a custom WhatsApp widget to your lock screen. Unfortunately, Android 5.0 Lollipop killed lock screen widgets and replaced them with heads up notifications that also work on the lock screen. Not all devices show all notifications though: LG famously copped criticism for only showing two notifications because it needed the rest of the lock screen space for its Knock Code.
If you unlock your device from the lock screen with the WhatsApp widget installed, the next time you unlock your lock screen, the WhatsApp widget will appear as the default. You can also unlock from a different lock screen to have another widget be the one you see when you unlock. Older (and newer) versions of Android do not support lock screen widgets, although it is still possible with apps such as Notifidgets.
How to get a WhatsApp widget on Galaxy devices
Galaxy devices running KitKat versions of Android give you the ability to set up lock screen widgets just like stock Android (Android Lollipop killed lock screen widgets on Galaxy devices too), but you can also add a WhatsApp shortcut to your lock screen if you prefer that.
Just go to Settings > Lock screen > Lock screen options and turn on the Shortcuts switch, then tap Shortcuts and choose WhatsApp from the list.
Having problems?
One way to get around this is to install an app such as NiLS or WidgetLocker, both of which are nice lock screen widget managers. You'll probably have to remove the default clock widget first though.
Download DynamicNotifications
Final reminder on security
Keep in mind that enabling lock screen widgets makes potentially sensitive information visible from a locked device, so either decide carefully which apps are accessible from the lock screen, or only allow your widget manager to show notifications from apps you don't mind being public.
In more recent versions of Android including Lollipop and Marshmallow, lock screen notifications are a default part of the system, but you can manage how much information is displayed on your lock screen.
While the convenience of not having to unlock your device to read WhatsApp messages sounds tempting, you should always seriously consider the issue of those messages being freely visible to anyone who picks up your phone
