What are Modem Lights?

Malcolm Tatum
Malcolm Tatum

Modem lights are simply the lights that are found on external modems. Depending on whether the lights are dark, activated and steady, or flashing, each modem light will provide an indication of the activity that is currently taking place between the modem and the connected computer hard drive. The current status of the modem lights helps the end user to know whether a connection is established, if the connection is active, or if the connection has dropped for some reason.

A modem.
A modem.

The activity of modem lights is usually referred to as handshaking. Essentially, when the modem is in use, the device is interacting with the computer. The modem receives input from the computer and in turn provides the hard drive with an influx of data as well. Both devices confirm receipt of data received and commands issued by the other. In this sense, the handshake is not unlike a gesture between two individuals who have agreed to an exchange or a plan of action.

Modern modems allow home computers to transmit faxes.
Modern modems allow home computers to transmit faxes.

This interaction or handshake that is signified by modem lights is made possible by the presence of the Universal Asynchronous Receiver/Transmitter that is found on the hard drive of the computer. The UART microchip is what actually allows the computer to talk to the modem, and to process data received from the modem. Without the presence of the UART, it is impossible to establish rapport with an external modem.

There are several types of modem lights found on the standard external modem. The AA, or auto answer light, signifies that the modem is engaged and ready to receive an inbound call. The CD, or carrier detector light, acknowledges that the computer and the modem have achieved a connection and communication back and forth is now possible. The HS, or high speed light, will be lit if the modem is prepared to transfer data at a relatively quick pace. Finally, the MR, or modem ready light, allows the end user to know that the modem is set for operation.

The series of modem lights found on a standard external modem help the end user to be able to monitor the current status of the connection at all times. In the event that the connection between the computer and the modem is broken, it normally takes nothing more than a quick reset of the modem and using a key, switch, or button on the modem to begin the process of re-establishing the connection.

A variety of lights will be found on the back of an external modem.
A variety of lights will be found on the back of an external modem.
Malcolm Tatum
Malcolm Tatum

After many years in the teleconferencing industry, Michael decided to embrace his passion for trivia, research, and writing by becoming a full-time freelance writer. Since then, he has contributed articles to a variety of print and online publications, including EasyTechJunkie, and his work has also appeared in poetry collections, devotional anthologies, and several newspapers. Malcolm’s other interests include collecting vinyl records, minor league baseball, and cycling.

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Discussion Comments


@starrynight - That sounds extremely annoying. Also, sticking a pen into a hole on an electrical device just doesn't sound safe to me. I'm really surprised that was the way the modem was supposed to be reset.

Personally, I'm glad modems have lights that tell us what is going on. I just always hope when I look at my modem for all the lights to be green!


I used to have a lot of problems with my old internet provider. Our internet would just go out without warning! It would usually turn out to be a problem with the modem, namely that the modem wasn't "talking" to the computer for whatever reason.

Normally, the carrier detection light would turn from green to red, and we would have to reset the modem. This was an especially annoying process as there wasn't a reset button on the modem exactly. There was a little hole you would have to stick a pen or something else small into. You would then have to hold it there for about thirty seconds, and hope the modem would reset.

I ended up switching to a new provider with a seemingly better modem and I've had a lot less internet issues since then.


@ElizaBennett - That's funny! At our house, we are also very familiar with the orange light phenomenon.

A few years back, we had DSL service and we had our own modem, which we had bought in another city. Our Internet went down completely even tough no modem lights were blinking. We had terrible trouble getting someone to come out and fix it because they kept insisting we would have to do a weekday from 8-12 or 1-5, and I kept insisting that since we paid for the service and they weren't providing it, they needed to find a time when we wouldn't have to take off work. I felt very strong that this was their problem and they needed to fix it.

They finally set us up for Saturday, but still didn't show up and I had to call and be nasty again.

When the person finally showed up, it turns out that our modem had gone bad. Oops!


In my house, we don't know the names for all the lights or what speed our internet is; we just have "the one that is sometimes orange" while all the others are green. And when that light is orange, there's no Internet. Sometimes resetting the modem will work, and sometimes it won't.

When it's flashing orange, that means it's thinking about it and we might get the Internet back as soon it's done thinking--or we might not. I can't tell you how many times I've stood in fron the modem watching that blinking light and holding my breath!

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