Embr's air-conditioner for your wrist: the verdict

The Embr Wave serves as a personal thermostat. Photo / Supplied.

I really wanted the Wave to work.

It's a bracelet, created by US startup Embr, that heats or cools the veins on your risk - warming or cooling your whole body in the process. Or so I hoped.

I saw it as the answer to my heatwave suffering and, after seeing it featured in US media, badgered its CEO via LinkedIn.

A review unit arrived at NZME Towers a few days later. I immediately charged it and slipped it on my wrist.

There was a pleasant cold sensation. Within seconds it was like an icecube touching my skin, but not as harsh. I imagined my body was cooling. But a few hours later, as I queued for a ferry in the blazing sun, I tried it again. To be honest, it made stuff all difference.

I tried it again later, lying in bed, with the sun gone down but the room hot and stuffy in the still Auckland air. Again, I struggled to feel any effect. Ditto when I tried the warming function while standing in a beer fridge at a bottle store near the Herald.

I wouldn't pay $12.99 for the Wave, let alone its list price of US$299 ($433). Some US critics have been kinder (see the clip below), but the general consensus is that it doesn't make enough of a difference to justify its price tag.

I also suffered an unexpected annoyance: When in cooling mode, the Wave's aluminum top heats up - not enough to burn you, but enough to wince and say "ouch" if you accidentally knock it forward to it makes contact with palm (which is easy to do).

The Embr Wave serves as a personal thermostat. Photo / Supplied.

Because of this heating, Embr warns you not to cover the Wave with your sleeve. This makes it impossible to be discreet. While I was standing it the ferry queue, it drew what I imagined to be derisive stares. Some probably thought it was useless New Age tat - and, to be blunt, they were probably right.

More ignomy followed as Auckland man Brett Roberts tweeted that it looked like I was wearing a home detention bracelet.

The Wave is also not waterproof or shockproof.

It charges via a micro USB cable. One charge will last 20 to 50 cooling or warming sessions, each incorporating technology apparently designed to regulate the temperature on NASA's Curiosity Rover as it faced Martian extremes.

Warming sessions last for three minutes, then you have to give the Wave a rest for a couple of minutes before another go, which is frustrating.

There are buttons on the Wave for almost immediate cooling or warming, but you can also calibrate things more finely if you download Embr's app.

Home detention just got a lot more colourful.

— Brett Roberts (@brettroberts) February 11, 2019

The veins on your wrist - being close to the surface - are particularly sensitive to temperature changes. But Embr concedes the Wave can't change your core body temperature (there's lots of precationary fine print to that effect in its manual). And I didn't find it managed to trick my body into feeling warmer or cooler.

I had dreams of the wave perfectly regulating my temperature as I tried to sleep. But in practice, it's not more effective than slapping a cold flannel on your face - which is a whole lot cheaper.