This circuit would be connected to an electronic door striker, or to a relay which would control an electronic door strike.
(Go to McMaster.com and search for Electric Door Strike.) This is the the hole in the doorframe which the door latch goes into. When power is applied to it, it allow the door to open when power to the strike is applied.
Or, through a relay you could operate a garage door opener or a solenoid operated latch.
The circuit is pretty simple.
On power up, IC Q0 output is activated. If switch #1 is pressed, it applies a "1" signal to the other side, causing transistor Q1 to turn on, clocking the IC to the next count.
Then, IC Q1 is activated and Q0 is off. Now switch #7 must be pressed to increment the counter.
This works unill the signal works it's way down until the IC's Q7 is activated. This turns on the output transistor Q2, lighting the LED D3 and powering the output relay at terminals X - X.
If the correct button isn't pressed for 4 seconds, the counter is reset by Q1 and D1. Even after the correct sequence is activated, this reset circuit will reset the output after about 4 seconds.
It is kind of a cool little circuit, but it does have to be built, hardwired and hard coded. A simple keypad for a garage door opener would be a lot easier to use, even on non-door applications.