UNIHAND heat levels

Three levels, counted in red lights

Each unit offers three levels, and the number of red lights tells you which one is on. Low holds 95-⁠107.5 °F, Medium holds 104-⁠118.5 °F, and High holds 118.5-⁠130 °F. The top of High, 130 °F, is the most heat the warmer gives.

The ranges meet at their edges. Medium begins at 104 °F, a little below the top of Low, and High picks up at 118.5 °F where Medium ends. You can move between them with the orange button as often as the day needs.

Picking a level for where the warmer sits

Think first about what lies between the warmer and your skin. Inside a closed mitten, with a layer of knit around it, Low or Medium is usually plenty. In a thin coat pocket on a windy street, Medium keeps up better. Held in a bare palm for a quick warm-up, High works fast.

Then think about how long you need it. A ten-minute wait for the bus can spend battery freely. A morning in a cold seat cannot. If your hands feel hot, or the skin under the warmer turns red, drop a level or put the unit away for a while.

Your fingers should feel the heat clearly. If they cannot, because of numbness, nerve damage or cold that has gone too deep, the warmer cannot report back through them. The NIDDK notes that nerve damage from diabetes can make it hard to sense temperature in the hands, so ask your doctor before using any heat source.

What the up-to hours promise and what they do not

Our temperature chart gives each level a figure: up to 20 hours on Low, up to 14 on Medium and up to 8.5 on High. Those are our numbers for one unit running on one level, and they are ceilings. Most real days land under them.

Three things eat into the hours. Cold air drains the battery faster, wind pulls heat off the shell, and switching on and off many times adds up. Plan your day from the shorter end and treat any time beyond it as a bonus. If the forecast calls for wind, plan as though the day will run short.

Why cold and wind cut the hours

A cold battery has less to give. By Battery University's figures, a battery that gives 100 percent at 80 °F typically manages around 50 percent at 0 °F, because cold raises its internal resistance. Our warmers use a lithium battery, so the same rule pushes against you on the coldest days.

Wind works on the shell. The National Weather Service explains that wind cannot make an object colder than the air, but it drags the object down to the air temperature faster. A warmer in an open pocket on a windy ridge loses heat faster and works harder to hold its level.

You can push back on both. Carry the unit close to your body, in an inner pocket, where it stays warm and out of the wind. Our article on keeping hands warm outdoors covers mittens, liners and dry layers.

What the AI chip does at each level

The part we call the AI chip pairs a temperature sensor with a controller. It measures how warm things are where the shell meets your hand, then adjusts the heat to keep the level you chose. When the air around you cools, it works to hold the range rather than letting it slide.

It does not learn your habits, pick a level for you or do anything for your circulation. You choose the level with the button. The chip keeps that choice steady.

The pairs on this page are part of the UNIHAND lineup, and the four colors above were picked for heat levels. Compare them side by side.