(Pocket-lint) - Ring will be introducing a new, much-requested feature alongside its new Video Doorbell 3 Plus device in April: Ring Pre-Roll.

It effectively grabs a short piece of video before the doorbell detects motion, so you can see why you are getting an alert in real-time.

Here is an explanation of Pre-Roll, how it works and whether it is coming to devices other than the Doorbell 3 Plus.

What is Ring Pre-Roll and how does it work?

Ring Pre-Roll is a new software feature that is launching with the Ring Video Doorbell 3 Plus.

It's the first time such pre-record functionality will appear on a battery-operated smart doorbell.

It basically shows the four seconds of activity that occurred before a motion alert is triggered, allowing you to see the exact reason for the notification rather than just the moments after (as is the case right now).

It works through an all-new three-camera module, designed specifically for Pre-Roll and included in the doorbell in addition to the normal main 1080p camera system.

This new module works more like a time-lapse camera, effectively capturing stills over a slow frame rate, in a much lower resolution and in black-and-white. This saves on power use greatly, so can be activated without any noticeable drop in battery life over other models.

Essentially, this pre-record mode runs constantly, even when the doorbell is not in use. As soon as motion is detected, it grabs the last four seconds of the constant separate feed and presents it in a picture-in-picture box over the live 1080p doorbell video. You can also swap the two videos to make the PIP footage larger.

Those with Ring Protect accounts will be able to store and view Pre-Roll videos in the cloud, stitched onto the motion recordings.

Will Ring Pre-Roll be available on older Ring Video Doorbells?

Sadly, because Pre-Roll requires the use of the new three-camera module that can only be found in the Ring Video Doorbell 3 Plus, it won't be coming to previous models.

It won't even be available for the standard Ring Video Doorbell 3 - also launching in April.

So, if you interested in the new feature, you'll need to spend £199 on the Plus version (the standard model will be priced at £179 in the UK).

Those with wired Ring Doorbells have had a similar feature since 2017 - such as the Pro and Elite.

Writing by Rik Henderson.