Biological sensors
All living organisms contain biological sensors with functions similar to those of the mechanical devices described. Most of these are specialized cells that are sensitive to:
light, motion, temperature, magnetic fields, gravity, humidity, vibration, pressure, electrical fields, sound, and other physical aspects of the external environment;
physical aspects of the internal environment, such as stretch, motion of the organism, and position of appendages (proprioception);
an enormous array of environmental molecules, including toxins, nutrients, and pheromones;
many aspects of the internal metabolic milieu, such as glucose level, oxygen level, or osmolality;
an equally varied range of internal signal molecules, such as hormones, neurotransmitters, and cytokines;
and even the differences between proteins of the organism itself and of the environment or alien creatures.
Artificial sensors that mimic biological sensors by using a biological sensitive component, are called biosensors.
The human senses are examples of specialized neuronal sensors. See Sense.