An anti-intrusion system is battery powered and is activated by pressing the only available button.

In the given state transition diagram, we need to identify the minimum number of test cases required to cover every unique sequence of exactly 4 states/3 transitions starting and ending in the "Inactive" state.

The states are:

Inactive

Active

Alert Mode

Alarm bell rings

Inactive -> Active -> Inactive -> Active -> Inactive

Sequence: Press Button, Enter PIN, Press Button, Enter PIN

Inactive -> Active -> Alert Mode -> Inactive

Sequence: Press Button, Sensor Activated, Enter PIN

Inactive -> Active -> Alert Mode -> Alarm bell rings -> Inactive

Sequence: Press Button, Sensor Activated, Timeout expired, Press Button

Test Case Analysis:These sequences cover every unique combination of exactly 4 states and 3 transitions starting and ending in the "Inactive" state.