The Gas Sentinel

Gas does not smell. Not really. The smell everyone associates with a gas leak — that sharp, unpleasant warning — is a chemical that gas companies add on purpose. The gas itself, LPG, is odourless. The stink is added so humans can detect a leak before it becomes dangerous. It works. Mostly. People smell it and act. Windows open. Flames go out. Everyone leaves. The problem is: people are not always there. People sleep through it. People step outside and do not come back in time. People are at the other end of a large house, or upstairs, or distracted. The nose that catches a gas leak needs to be in the same room as the gas, awake at all hours, impossible to distract, and loud enough to reach wherever the people are. It is not a person. A gas sensor is a small component whose electrical resistance changes when it encounters certain gases. At clean air, its resistance sits at one level. When gas arrives — even a faint trace, well before a human would smell it — the resistance shifts. That shift in resistance can be read as a voltage. That voltage can be compared to a set threshold. When it crosses the threshold, a buzzer fires. Silent below the line. Loud above it. No lunch breaks. No getting used to the smell. Today, your team is going to build one.