Chances are that I’m not going to patent what I jokingly referred to as a “grass height detector” on my Facebook page. But there is a chance that your relative developed an actual invention and received a patent for it. If the product didn’t make your relative’s life, there may have been no mention of it to later family members.
US patent applications can be searched on Google Patents. Older applications may give your ancestor’s state and county of residence and indicate whether or not the applicant was a United States citizen. There may be grass height detectors listed, but none of them are mine.