What do UV rays, carbon monoxide, radiation, and nitrate ions have in common? Besides sounding like things we want to run away from, all are environmental impurities that are hard for the naked eye to detect. Thankfully, hardware startups have been busy working on consumer-friendly smart sensors that reveal what our bodies, gardens, and produce are exposed to on a daily basis. Even Apple has jumped on the sensor bandwagon and is aiming to pack them into the next iPhone. But there’s no need to wait for that device’s release. Here are four smart sensors that can help you jump in the driver’s seat and figure out what chemicals and toxins you are up against.