Let's talk about Dhoondte Reh Jaoge first. Towards the climax of the film when the fraud characters played by Paresh Rawal and Kunal Khemu land in jail, they start exploring plans for the future. This is where they come across an idea of duping their fellow jail inmates into making another film. Though the duo is set free after a year, the film does give good enough hints that together, they may well go back to their funny and fraudulent ways and continue duping investors.
The possibility of a sequence is just an indication in Dhoondte Reh Jaoge but in case of 13B the message is loud and clear. The film makes a point that human body is the most complex machinery that the world has ever seen. On this premise, the movie raises a simple question - 'If one can trust spirits to use a human body as a medium to interact with the outside world, why can't one trust them to enter a machine and use it as a medium?' No wonder, a TV set becomes a medium for spirits in 13B.
So where is this all leading to a sequel? Well, towards the end of the film, when it is believed that 'sab khairiyat hai', the character played by Madhavan gets a call. The caller? A spirit! The message - 'If we could get into the TV, we could as well get into the mobile phones as well. The game is not yet over!'
So is the game really over? Now it all depends upon the final box office outcome of the two films because that will be the deciding factor for the sequels to be eventually planned and executed!