In most places, the device would make for an unusual garden accessory. But it is a common sight in Stuttgart, southwest Germany, where hundreds of the gadgets hang in homes and backyards across the city.
Jallow, 55, is a lively mother of two who has lived in Stuttgart for 30 years. She uses her sensor every day to check the level of pollution -- but it's not just the numbers that tell her the air is dirty. On bad days, she can see the pollutants on the sensor itself.
"You can feel it," she told CNN last year. "When you go outside, you notice it. You get breathing problems, your throat hurts, you start being short of breath easier."
The air in Jallow's neighborhood is some of the most polluted in the country
, with levels of particulate matter and nitrogen dioxide (NO2) -- both products of diesel vehicles -- often reaching dangerous levels.