In this world that we share with them, they became unintended sentinels for the consequences of pollutant exposure, developing similar conditions to humans, and even earlier. This review focuses on the human-pet interaction and on the effects of the environment pets share with us. Alongside other species, canine and feline companions are veritable models in human medical research. The latency period for showing chronic exposure effects to pollutants is just a few years in them, compared to considerably more, decades in humans. Comparing the serum values of man's best friends to ours can indicate the degree of poisonous lead-load we are exposed to, for example, and of other substances as well. We can find 2.4 times higher perfluorochemicals from stain- and grease-proof coatings in canine companions, 23 times higher values for PBDEs in cats, and five times more mercury compared to the average levels obtained in humans. All these represent early warning signals. Taking into account all these, and the animal welfare orientation of today’s society, finding non-invasive methods to detect the degree of environmental pollution in our animals becomes paramount, alongside with the need to raise awareness on the risks carried by certain chemicals we knowingly use.