You can also classically condition a bee with food rewards to extend its mouthparts whenever it detects a specific odor. You then put the plastic bee cartridge into a device such that when the mouthparts extend, an LED illuminates.
Cheaper than dog noses, but requires a sample of the target odor and some training time. It is conceivable that the "most wanted" could each have thousands of bees trained on their scents, and then those swarms could be divided up onto plastic cassettes, which would each be loaded onto a lamppost. If the targets go near any lamppost, their bee in it tattles its location in real time. The disadvantage is, of course, that you have to go around swapping out old and dead bees for live, fresh ones all the time.
An electronic nose can just report its odor profile, and a central processing server can attempt to match and track targets. All that needs is a bit more bandwidth. But it is likely slower and lacking specificity. You could likely smell explosives or bomb making residues or gunshots or narcotics, but not specifically track Suspect X across the city. That kind of precision would require that people line up at the lamppost to be swabbed, and their swab vaporized and run through a gas chromatograph for a minute or two, which I don't see happening, even in authoritarian Singapore.
Cheaper than dog noses, but requires a sample of the target odor and some training time. It is conceivable that the "most wanted" could each have thousands of bees trained on their scents, and then those swarms could be divided up onto plastic cassettes, which would each be loaded onto a lamppost. If the targets go near any lamppost, their bee in it tattles its location in real time. The disadvantage is, of course, that you have to go around swapping out old and dead bees for live, fresh ones all the time.
An electronic nose can just report its odor profile, and a central processing server can attempt to match and track targets. All that needs is a bit more bandwidth. But it is likely slower and lacking specificity. You could likely smell explosives or bomb making residues or gunshots or narcotics, but not specifically track Suspect X across the city. That kind of precision would require that people line up at the lamppost to be swabbed, and their swab vaporized and run through a gas chromatograph for a minute or two, which I don't see happening, even in authoritarian Singapore.