Don't know if these are well known or not, but found a neat gizmo that has been handy while cycling. Its a little plastic card with a suction cup for application, that gives a continuous reading of ammonia levels by four readings.
Safe, alert, alarm, toxic
Specs for ammonia levels are included in package so you know approx. level for the 4 readings.
Safe, alert, alarm, toxic
Specs for ammonia levels are included in package so you know approx. level for the 4 readings.