Services such as LivesOn and DeadSocial plan to keep your friends and family updated on your Twitter and Facebook pages, even after you have passed away

Forget Ouija boards. If you want to communicate with the dead these days, all you need is Twitter. Much like last week's episode of Charlie Brooker's Black Mirror, in which a grieving woman uses a digital service to communicate with her deceased boyfriend, social media is already bridging the gap between the living and the dead.

Launching in March is a new Twitter app called LivesOn. The service uses Twitter bots powered by algorithms that analyse your online behaviour and learn how you speak, so it can keep on scouring the internet, favouriting tweets and posting the sort of links you like, creating a personal digital afterlife. As its tagline explains: "When your heart stops beating, you'll keep tweeting."

"It divides people on a gut level, before you even get to the philosophical and ethical arguments," says Dave Bedwood, creative partner of Lean Mean Fighting Machine, the London-based ad agency that is developing it.

"It offends some, and delights others. Imagine if people started to see it as a legitimate but small way to live on. Cryogenics costs a fortune; this is free and I'd bet it will work better than a frozen head."

Mia Smith, a business owner in her mid-40s, has already registered her interest. For her, it is the chance to have a "kind of ironic legacy" that drew her in. "But I'm not sure who'd be interested in reading a computer-generated 'me'," she says. "In the cold light of day, it is a very conceited thing to do."

The growth of "digital legacies" is already throwing up legal and ethical issues: it's a violation of many websites' terms of service for surviving relatives to go on using your passwords; and digital libraries of messages and photographs can't easily be passed on unless the correct consent is in place. Facebook has already gone to court to oppose the idea that families can force it to hand over data.

Anyone signing up for LivesOn is asked to nominate an executor who will have control of the account. Another service, DeadSocial, puts the power in the deceased's hands. It is a "digital legacy tool" that lets you set up a series of messages to be sent out posthumously, via Facebook and Twitter. "It allows you to enhance your memories, extend relationships and create something of value for those who are still alive," explains creator James Norris, who has been taking the emotional aspect of the app seriously; his team have been consulting with a doctor specialising in end-of-life care.

However, the impact that such sites could have on the bereavement process is unknown. For Pamela Rutledge, director of the Media Psychology Research Centre in Massachusetts, sites such as DeadSocial are a "digital extension" of people leaving letters to be read after they die. For her, apps that create artificial messages on behalf of the deceased are more problematic. "What do we do if someone uses this new extension of time in a way that torments or stalks its receivers?" asks Rutledge. "Death is the ultimate lack of accountability." And if the future of social media platforms is one haunted by digital ghosts in the machine, would you still log on?