He could use an analogue multiplexer, but a better option would probably be to use multiple ESP devices.
In reality, these sensors aren’t likely to be in the same physical place within the house, so multiple devices, with each located next to the area where the sensor is needed, is probably a better solution.
However, it seems that @ykilicaslan needs to invest some time in learning how to code, and how best to use Blynk, so I doubt that his alarm system will actually materialise.
On the subject of alarms, I came across this YouTube video the other day:
It seems like a really neat solution to adding IoT notifications to a standard battery powered alarm. If I was doing this then I’d probably go with the MQTT notification as described in the video, but it would be just as easy to add a Blynk notification, or use a Blynk API call.
Pete.