Hi gada,
First of all, when posting on the forum, always put your sketch in code tags. See the "#" button when you edit/post your topic. Edit your original post and put the tags in please.
You mention 2 sensors, but your sketch only gives the pin number for one. What happens with the second sensor?
How will you switch off the alarm? Do you mean you will cut the power to the Attiny?
For your 3 minute off/1 minute on repeating alarm, you can use delay() with longer values. To get this part of the sketch to repeat itself, see the while() command.
Paul