If you can't do that, WTF are you doing sitting up front in an airliner?
...or a C172 for that matter. How many more bells and whistles do we need? A modern aircraft will give a visual, aural, then (excluding Airbii) tactile warning that you're getting slow.
One wonders how those courageous Cessna 172 pilots manage to keep those things in the air with only an airspeed indicator and a stall horn.