Setting up call blocking on someone else's phone: a matrix by phone type

Find the phone in front of you in the first column. Each row says what to switch on, where it lives, how to prove it works and what can go wrong. The notes under the table explain each row.

Row by row

iPhone

Turn on Silence Unknown Callers, then spend more time on Contacts than on the switch. Add family, the doctor, the pharmacy, the home health agency, a taxi service and any regular helper. Silenced numbers that are in Contacts still ring, which is what makes the setting comfortable. Also check Settings > Phone > Call Blocking & Identification, where a carrier's filter app may appear, and Settings > Messages > Filter Unknown Senders, which sorts texts from strangers into a separate list. Finally open Voicemail, set a greeting and make sure the mailbox is not full. If a path does not exist on the screen, search Settings for the phrase.

Android with the Google Phone app

Open the app, tap the three-dot menu, choose Settings, and switch on the spam filter under Caller ID & spam. Blocked numbers lets you add a persistent caller, though blocking one number rarely helps for long. If the handset offers Call Screen, it lets the assistant answer unknown calls and show a transcript. Not every phone or region has it. Add the trusted numbers to Contacts, then call the phone from yours and let it ring out to confirm voicemail works. Google's own support pages describe the current menus.

Android with a maker's own phone app

Samsung, Motorola and others sometimes ship their own app. If the Phone app does not look like Google's, open its settings and hunt for the words "block" and "spam". Describe the path you found on the sheet you leave behind, because nobody will remember it.

Flip phone

There is no menu to flip. Ask the carrier what call filtering is available on that line, what it costs and how to switch it on, and keep Contacts tidy with a working voicemail greeting.

Copper landline

A basic landline cannot silence unknown callers. The options, from the box that only lets saved numbers ring to a large-button phone with a short contact list, are compared in the landline blocker conversations. Whichever you pick, the setup order is the same: plug the box into the wall, the phone into the box, then the power adapter.

Home line over the internet

The options often differ from a copper line and many plug-in boxes need a compatible adapter. Check the compatibility notes or ask the seller, and ask the provider whether it blocks or labels calls.

Before you touch anything

Start with a conversation, not a screwdriver. Say in a sentence or two what you plan to do and why: "Strangers will go to voicemail, and the calls that matter will still ring." Then ask whether that is acceptable. People keep rules they helped choose, and people who find out later feel watched. Gather the phone, the passcode, the carrier's name and a pen. On an iPhone, Settings > General > About shows the model and software version, and on Android it is Settings > About phone. Decide who will know the passcode afterwards, and make sure the owner and a family member both know what you changed.

The sheet that stays by the phone

A written record keeps your help from becoming a mystery. Include these, tape one copy near the phone and give another to a family member:

• The date and who did the work.
• What changed, for example "Silence Unknown Callers on, voicemail greeting recorded".
• The names of the trusted numbers added. The numbers themselves live in Contacts.
• How to undo it, for example Settings > Phone > Silence Unknown Callers > off.
• Who to call, with a name and number in large print.

The sheet is also the best place for the rule from the cheat sheet for helping a parent: if it is urgent, hang up and call someone you know.

After you leave: test, then recheck

1. Call the phone from your own number while you are saved in Contacts. It should ring.
2. Call again from a number that is not saved. On an iPhone with Silence Unknown Callers it should go to voicemail, and on Android it should behave as the screening setting dictates.
3. Leave a short voicemail and confirm the person can find and play it.
4. Ask them to call you, so you can see how they dial from Contacts. If they cannot find the voicemail screen with you watching, they will not find it alone at nine at night.

Recheck about monthly at first, then every few months, since software updates sometimes rename or reset options. The usual mistakes are silencing before the doctor is saved, forgetting a voicemail greeting, blocking numbers from an online list without checking each one, and deciding for the person without explaining. A blocker is a filter, not a judge. A spam label is a carrier's estimate, and an unlabeled call is not thereby safe.

If the person hesitates, start with one setting and leave the rest for another visit. For a relative with memory loss, the memory-loss mistakes list goes deeper. If you are caring for a client or neighbor rather than a relative, agree in writing with them, and their family or agency, what you will and will not touch, and never go through messages or accounts beyond the settings you were asked to set.