The phrase "bullshit meter" refers to a figurative device or skill that allows someone to recognize or detect when something is not truthful or misleading. It means being able to tell when someone is lying or trying to deceive you. Full definition
Updated January, 2011 The first thing to remember about working with the news media is that reporters are bombarded with information and that the good ones consequently quickly develop a sensitive bullshit meter. (epolitics.com)
In fact, at this point my bullshit meter is a finely tuned instrument. (ericward.com)
Who would I be without my furrowed brow and bullshit meter? (mindbodygreen.com)