Durex’s first e-commerce app in the UK doubles as an erotic manual on how to use your purchases – that you watch via the ad.

Havas’ new ad has a secret other life. The TV ad is a somewhat suggestive story about a courier delivering condoms to an apartment block. Glimpses of the building’s occupants, through windows and glass doors for example, hint that most of them are having sex.

If you download the app and point your phone or tablet at the TV or computer screen where the ad is playing, you can watch a synchronised second screen on which what the occupants are doing ‘behind closed doors’ is screening.

Havas Worldwide’s London office developed both the Durex Explore app, which functions as a mobile version of the e-commerce site, and the commercial.

The campaign was conceived to promote the brand’s first, dedicated UK e-commerce site and to encourage people to be more confident about experimenting with products, including sex toys.

“We knew we might have some challenges showing all the products on the site in a TV ad and the dual screen idea gets your around this,” explained Michael Olaye, Havas’ head of technology and innovation.

The app uses a mobile device’s camera and microphone to detect not just that the ad is playing on a nearby screen but to precisely sync the mobile screen to the exact corresponding point in the original video.

“A particular challenge was getting the app to distinguish between two different versions of the TV ad—one 50 seconds, the other 30 seconds long,” Olaye added. The agency solved this by using frame by tracking and barely perceptible soundtrack cues.

The ad makes use of the fact that so many people watch TV and another screen at the same time now.

“This isn’t just an app to sync different versions of a TV ad, it also features social feeds and links directly into the Durex e-commerce store,” Olaye noted.

“The idea behind this was to get people to explore different aspects of their sex life. Because of films and advertising, great sex is sometimes seen as something for someone else—beautiful people and sexual athletes. This campaign is about saying: exploring your sex life is something for everybody,” Alasdair Graham, Havas’ global executive creative director for Durex’s owner, Reckitt Benckiser.

Durex Explore is available from iTunes and Google Play, and was promoted with a launch event, push notifications and a call to action advising viewers of the ad on TV in the UK November 28 and online November 26.