Caller ID box vs built-in caller ID on a landline: a buyer's checklist

Stand next to the phone with your latest bill in your hand. Everything below can be ticked off in about twenty minutes, most of it costs nothing, and the first group tells you whether you should buy anything at all. A caller ID box and a handset with a built-in screen read the same signal from the same carrier, so the choice is about where the screen sits, who can see it and what extras come along.

Before you buy anything

• Confirm caller ID is part of your plan. The box or the handset only decodes what the carrier sends, and if the line carries no caller ID service, no device will invent it.
• Find out whether it includes names or only numbers. Some providers sell number-only service and treat names as a paid add-on. A new device will not add one, so ask the carrier whether name display can be switched on. The reasons names look so strange are worth a read first.
• Note which phone the household actually answers. A screen on the phone nobody uses is wasted money.
• Read the manual for your model. Specifications vary widely between boxes and handsets, and I would rather you check than trust a table about all devices.

When a separate box makes sense

• You own an old phone with no screen. A rotary dial or a heavy beige desk set gets a display from a box that sits beside it, without replacing a thing.
• An older relative answers the phone. Choose the biggest, clearest screen over the cleverest features. A small cordless display is hard to read from a chair.
• You want one list for the whole line. A box shows calls from every phone plugged in around the house, while a built-in display only helps whoever holds that handset.
• The power source suits you. Boxes run on batteries or an adapter; a weak battery can make a display unreliable.
• The call history is big enough. Stored lists vary by model, and a full memory can drop the newest calls on some.

When a built-in display is enough

• Your handset already shows numbers and names, and you are happy. Keep it. There is nothing to plug in, because the same decoder is inside the phone.
• The set shares call history across handsets. Many cordless sets do this for all the handsets on one base.
• It has a phonebook and a block list. Many cordless sets include both, which a plain box may lack.
• The screen is backlit and readable. Check this in the room where the phone lives, not in the shop. A block list on either kind of device is a convenience and not a guarantee: some act only after the first ring, because the number is not known until then, so see what the cordless block button really does.

Before you pay

• Price name display against a new gadget. If your line sends numbers only, a small monthly fee for names may cost less than a device that still shows only digits.
• Keep what you have if it works. A handset you already read at a glance is worth more than a new box with features you will not use.
• Check you can return it. Screens that look fine in a shop can be hard to read beside a lamp at night, and a return window lets you find out.
• Skip the box if your only complaint is volume. A display tells you who is calling and does nothing to stop the ringing; blocking is a different job.

Setting it up on an older line

• Plug the box into the wall jack with the cable it came with. Then plug the phone into the second socket on the box, or plug the box into another jack in the same room.
• Add batteries or the adapter and set the date and time. Many boxes ask for both before they will log calls correctly.
• Ring it from a mobile. The box listens between the first and second ring, so the number should appear after the first ring. If nothing shows, check the jack and the plan before blaming the device.
• Put it at eye level beside the phone you use most. A screen you can read from your chair is a screen you will look at before reaching for the handset, and that glance is where most of the benefit lives.
• Clear the stored list now and then. Old numbers tell you little, and a clean list makes a fresh unknown call easy to spot.
• Leave a note beside it. "Unknown number, let it ring" changes behavior more reliably than any feature on the device.

When the screen is blank or odd

• Blank on every call, family included. Suspect the service or the connection, not the callers. Check the box is on the same line the calls come in on, and try another jack if the line runs through a splitter or filter.
• "Private" or "Anonymous." The caller asked for the number to be hidden. The carrier feature in anonymous call rejection turns those callers away before the phone rings.
• "Out of area" or "Unknown." Usually the number did not arrive, for technical reasons. It does not mean the caller is hiding.
• A familiar name that feels wrong. Caller ID shows what a call claims about itself, and it can be wrong or faked. Hang up and ring the organization back on a number you looked up yourself.
• You want real blocking, not only a display. A dedicated blocker or carrier tools do more than any display. The glossary of landline blocking terms shows the options side by side.