Juraj:
why web? why HTTP? plain socket communication will do it
OK. In the mean time this has been adequately dealt with. I'll just add that if the OP chooses to integrate the devices in an existing WLAN it is (a) very simple (without even making a new WLAN connection) to test the web server part using a standard PC browser or smartphone browser and (b) he can enhance the system later to, say, serve up a web page (for a standard browser client) which indicates the current status of the door he is monitoring, or the status of the dht22 temperature/humidity sensor mentioned in the OP.
Of course there are other ways of solving the problem, but using a well known method ensures that the OP can easily get support if something goes wrong.