What is LTE-M, and why would a ring use it?

LTE-M in one paragraph

LTE-M, also called LTE Cat-M1, is part of the 4G LTE family of mobile standards, designed for small devices that send a little data and must run for a long time on a small battery. It is slower than the 4G in your phone, around a megabit per second at most, but it reaches further indoors and lets a device sleep deeply between messages.

How it saves battery

• Deep sleep. A power-saving mode lets the device switch its radio off for long stretches while staying registered on the network.
• Listening in turns. Instead of listening all the time, the device wakes at agreed intervals to check whether the network has something for it.
• Short bursts. Small messages go out quickly, and the radio is off again.

What it cannot do

• Fast data. No video streaming; it is made for short messages.
• Calls, on many networks. Many operators offer no voice on LTE-M, and Lychnos Ring’s modem carries data only.
• Everywhere. Coverage depends on the country and the operator.

Why Lychnos Ring uses it

We wanted the ring to work without the phone. Wi-Fi would empty a ring’s battery quickly and work only in places you have set up; Bluetooth needs the phone nearby. LTE-M lets the ring send what you said and fetch the answer in short bursts, then sleep. Even so, the radio takes most of the ring’s daily energy in our design model, which is why answers are fetched in one go and played from memory. The eSIM inside means there is no card to insert: the ring is set up once from the phone app, and after that the phone can stay in your bag.

More on what that makes possible: a phone-free assistant.