Cooling wristbands work by leveraging the body's natural thermoregulation system, specifically by targeting the sensitive skin on the inner wrist. There are a few different technologies used:

1. Thermoelectric (Peltier) Devices:
How it works: These wristbands, like the Embr Wave, contain a compact thermoelectric heat pump. When activated, this pump uses electricity to create a temperature difference, making the part of the device touching your wrist feel cool (or warm, as many also have a warming function).
The "trick": The key here is not to actually change your core body temperature significantly, but to "trick" your brain. The inner wrist has a high density of thermoreceptors (temperature-sensitive nerves). When these nerves receive a strong cooling sensation, they send signals to the hypothalamus in the brain – the part responsible for regulating temperature, as well as emotion and stress. This sensation can then influence your perception of temperature throughout your body, making you feel cooler overall, even if your actual body temperature hasn't dropped drastically.
Dynamic sensations: Many advanced wristbands use "thermal waves" – pulses of cooling (or warming) rather than a constant temperature. This prevents your body from simply adapting to the sensation, maintaining the feeling of relief.

2. Evaporative Cooling:
How it works: Some simpler cooling wristbands use special fabrics or crystals that absorb water. When soaked in water, these materials gradually release the water through evaporation. As the water evaporates from the surface of the wristband, it draws heat away from your skin, creating a cooling effect.
Materials: These often use super-absorbent polymers or microfiber materials designed for efficient evaporation.
Effectiveness: These are generally less "active" than thermoelectric devices and rely on the ambient air for evaporation. They might require re-soaking to maintain their cooling effect.

3. Phase-Change Materials (PCMs) / Gel Packs:
How it works: Some wristbands incorporate specialized gels or PCMs that can be pre-chilled (in a refrigerator or freezer). These materials absorb heat as they warm up, providing a prolonged cooling sensation.
Mechanism: This is similar to how a cold pack works, providing a direct conductive cooling effect to the skin.

Why the wrist?
The inner wrist is a strategic location for cooling because it's a pulse point with blood vessels close to the surface and a high concentration of thermoreceptors. Applying cooling here can send signals to the brain that help regulate your overall perception of temperature.

In summary, while some cooling wristbands provide direct conductive or evaporative cooling to the skin, more advanced models leverage the body's neurological pathways to influence your perception of temperature, offering a sense of full-body relief from a localized sensation.