Explosive Detection Systems work more efficiently than dogs, and can detect more threats. Despite their moniker, an EDS can detect more than just explosives.
Baggage/cargo gets loaded in to an EDS system at a port (incl. an airport). Sometimes every bag gets screened, sometimes random bags get screened - depends on the port. The system then sends a series of radio waves across the baggage, with the waves targeting a set of detector crystals on the opposite side of the wave. The detector crystals receive the wave that is modulated by whatever material the wave went through. The crystals act as a transducer, that turn the the modulated waves in to an electronic signal. Its akin to a bag getting an MRI or CT-scan.
The signal is then run through a bunch of algorithms (that have generally been programmed manually). After the signal goes through the algorithm, the result is a digitized image of what sort of matter the wave actually went through as it traveled through the bag.
As the signal goes through the algorithms, the algorithms will be checking for types of threats. If the compound appears explosive, the image will be highlighted a certain way to alert the human screener. Most EDS systems can also check for radioactive materials, heavy metals (such as lead), wires (esp. loose wires), weapons, and magnets. Some units, especially those deployed at ports can also check for drugs. Some of the larger units can detect stowaway passengers.
The trouble with EDS units is their price. Someone has to pay for the units; the burden has generally been borne by us (taxpayers). The ports (including airports) also need sufficient physical space and infrastructure to support an array of them (multiple units are required to process a load of baggage in an efficient manner). EDS units are notoriously heavy. The smallest units are about 1600Kg (about 3500 pounds) and the larger ones are many times that amount. Most ports were not designed to support 50,000 - 100,000 pounds of detection equipment focused in one area, therefore remodeling is required to build a proper physical plant.
So, yes, the equipment is there, and use of it is growing...slowly.