How to add a WhatsApp widget to your lock screen

 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.

On a KitKat device, go into Settings > Lock screen and tick the box for Custom widgets. Then, lock your device's screen and from the lock screen, swipe to the side until you see the '+' symbol. Tap that and select WhatsApp from the list.

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 WhatsApp Widget On Galaxy Devices
Samsung uses a slightly different menu setup from stock Android, but customizing your lock screen widgets is simple enough.

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.