Most apps that react to where you are do it the easy way: the phone reports its position to a server, the server decides, the server sends a notification. That works, and it means someone else holds a record of everywhere you have been. Brain Buffer does the deciding on the phone.
You save a place — home, the office, a particular pharmacy — and the app keeps its coordinates and radius on the device. Every minute the background service compares your current position with that list locally. When you cross into a saved place, the phone itself raises the notification.
Nothing about that round trip involves us. There is no request to send, so there is no log of your position to keep, hand over, or lose.
A satellite fix is unreliable inside a building, so a place can also be recognised by the WiFi networks around it. The app stores a hash of each network identifier, never the identifier itself, and a place matches when at least two of them are visible.
A hash cannot be turned back into a network name or an address, so even the on-device record does not describe where you were — only whether this is the same somewhere as last time.
Reminders about a type of place — any pharmacy, any petrol station — cannot work this way, because the phone has no list of every pharmacy in the world. For those, and only those, the app asks the server what is nearby. Everything about your own saved places stays local; you can use the app without ever creating one of these.
You can set a reminder for someone in your family — the shopping, the tablets, the parcel. It fires on their phone, from their own copy of their own places. You never see where they are, and neither do we. A family here shares reminders, not locations.