SonarPen is a $30 iPad stylus that connects to the headphone jack

When the Apple Pencil was released, I was briefly outraged by the fact that it wasn’t supported by older iPads, then sucked it up and bought an iPad Pro. Hong Kong-based company Greenbulb is setting out to minimize this dilemma by crowdfunding SonarPen, a $30 stylus that senses pressure via the headphone jack, so it works with any iPad released after 2011.The SonarPen works by turning pressure information into sound waves sent to the iPad through the audio cable, which the iPad then inter