HK Call Guard — block Hong Kong spam calls without handing over your contacts

The privacy cost of most call blockers

Caller-identification apps work by crowdsourcing, and the crowd is you. The standard model is to upload your address book and your call log so the service can build its database — which means handing over the phone numbers of everyone you know, most of whom never agreed to it. For a tool whose entire purpose is reducing unwanted contact, that is a strange trade.

HK Call Guard keeps the matching local. The blocklist is stored on the phone, incoming numbers are checked against it on the device through Android's call screening role, and your contacts and call history stay where they are.

What the Hong Kong spam call blocker does

Screening, plus the tools for dealing with a number you have never seen before.

• On-device call screening. The app registers as Android's call screening service, so incoming numbers are checked against the local blocklist as they arrive — no lookup request goes out per call.
• Your own whitelist. Numbers you always want through, regardless of what any list says. Necessary because shared office lines and clinics do occasionally end up on public nuisance lists.
• Report a number. A nuisance number that got through can be reported and added, so the list improves in the direction that matters to you.
• An OCR scanner for screenshots. Point the scanner at a screenshot — a message, a missed-call notification, a suspicious page — and it extracts Hong Kong phone numbers on the device, recognising the 8-digit format starting 2, 3, 5, 6, 8 or 9 with or without a +852 or 00852 prefix and any spacing. It also looks for scam keywords in the text. This runs locally, so the screenshot is not uploaded to be read.
• SMS filtering. A filter screen for nuisance messages alongside the call blocking.
• Honest update reporting. When the blocklist updates, the app tells you how many entries were fetched and how many were actually new — including the case where nothing changed. That sounds pedantic; it exists because a silent “updated” message once hid a bug where the same data was returned every time.

Local matching, local scanning

The two operations that would normally justify a server — checking a number and reading a screenshot — both happen on the phone. Blocklist data is fetched as a dataset and stored locally rather than queried per call, and the OCR uses an on-device text recogniser.

The consequence is that the app cannot identify a number that is not on its list, which a cloud service sometimes can. That is the trade, stated plainly: less coverage on unknown numbers, in exchange for not becoming a source of everyone else's phone numbers.

Who it is for

Anyone in Hong Kong receiving several nuisance calls a week — which is most people with a local number. The volume is high enough that screening is worth setting up and low enough that a local list handles the bulk of it.

It particularly suits people who have considered a mainstream caller-ID app and stopped at the permission screen: professionals with client numbers in their contacts, anyone handling sensitive relationships, or simply anyone who read what the permission actually grants.

Permissions and privacy

The app uses Android's call screening role to see an incoming number, phone state to know a call is arriving, and photo access only when you choose a screenshot to scan. The blocklist is stored in a local database; updates are fetched as a dataset. Your contacts and call log are not read for upload.

Nuisance-number lists are compiled from public reporting and are never complete or perfectly accurate. Check the whitelist if a call you expected did not arrive. The app is free and ad-supported with an optional premium purchase.

Frequently asked questions

Does it upload my contacts or call history? No. Matching happens on the device against a locally stored blocklist. Your address book and call log are not uploaded.

How does it know a number is spam? It checks against a blocklist dataset held on the phone and refreshed periodically, plus any numbers you have reported or added yourself.

What is the screenshot scanner for? It reads a screenshot on the device and pulls out Hong Kong phone numbers and scam keywords — handy for checking a number in a message without retyping it. The image is not uploaded.

Can I stop it blocking a number I need? Yes. Add it to your whitelist and it always comes through, regardless of what any list says.

Will it catch every spam call? No. A local list cannot identify a number nobody has reported yet. That is the honest trade for not uploading your contacts.