Cut open mat and check insides with rusty knife. Then/or examine door locking mechanism.
You cut open the mat..

You made a mess, luckily you found a note.
Note
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" January 4th 1989. Hello there. If you are reading this, you must be from the future, or a guard... If you are from the future, I will help you...
There are several alarms around the building... Too bad there aren't any in your cell. Use your pocket knife, (You opened the mat with a pocket knife, right?) And Break off the blade. Once that is done, Shatter the window of the door, the big window isn't breakable.. Once you do that, it will alarm the guard outside.. Unless he got fired.. And you continue from there."
"Sincerely, Jack Fellowsome"
You do what he said to do....
Nothing happened. The guard must be out to lunch.
What do you do?