When we sniff, our sensors (in the nose) pick up molecules of gas and send messages to our brain for the appropriate decoding. Your dog is way more effective in picking up gas molecules and we have seen in the last two decades electronic noses that are getting more and more effective (some even more effective than your dog if you are interesting in picking up a specific scent).
The problem with electronic noses is that they are pretty bulky. This has to do with the technology used to pick up, detect and identify gas molecules.
One technology that is used is rotational spectroscopy. It is very effective in identifying gas molecules with high specificity (it does not confuse one type of molecule with another).
Present rotational spectrometers are made with semiconductor and circuitry that can generate the 100GHz waves that are used to detect specific molecule with a sensitivity in 10Khz band (the narrower the band the more specificity can be obtained). They are good but they are both bulky and costly.
At Dallas University researchers have been able to develop a rotational spectroscope that is very small, cheap and yet has very high specificity. They are reporting their result in a (highly) technical paper.
The system illustrated works in the 220-250GHz and, as seen in the image, its size is very small. At this very high frequency the wavelength is very short and hence the antenna can be very small too.
The system will first be used in industrial settings to detect the presence of dangerous gases and then in hospital environment to help in diagnoses of some types of cancer and then it will be used in pharmacies for cancer screening. Eventually, we might think of a day where these types of systems will become commonplace in our home, as today we have a thermometer.
The first programable noses should be available in 2018.