Privacy
LAST UPDATED 26 AUGUST 2026
This page describes what Cosydays actually does with your data. It is written to match the software rather than to cover every eventuality, so if something here disagrees with how the app behaves, the page is wrong and we want to know.
Cosydays is a cloud service, and it has to be. Weather-matched before-and-after verdicts, year-on-year history and comparison against similar homes cannot be computed on a phone: they need continuous collection while the app is closed, and — for the comparison — other people's data. Any older Cosydays material saying your keys stay on your device is out of date and wrong.
What Cosydays stores
Your account
An email address, and a password or a Google or Apple sign-in, held by Amazon Cognito. Cosydays never sees your password, and never sees your Google or Apple credentials.
Your Octopus connection
Your Octopus Energy account number and API key. The key is encrypted before it is written down and is used only to call Octopus Energy's own API on your behalf. It is never shown back to you in full and never leaves our servers except in a request to Octopus.
Readings from your heat pump
Collected on a schedule for as long as your account is connected:
- Half-hourly snapshots — flow and return temperatures, room temperature and setpoint per zone, hot water, mode, COP, and the controller's own status.
- Half-hourly electricity consumption from your smart meter.
- Octopus Energy's hourly heat-pump performance history, which reaches back roughly thirteen months.
- Your unit rates and standing charges, so costs are your real costs rather than an average.
- Outdoor temperature for your area, so a change can be judged against the weather it happened in.
What you type in
Changes you log — "turned the flow temperature down to 40°" and the like — with any note you add. These are the record every verdict is computed from.
Where it lives
On Amazon Web Services in the London region (eu-west-2), in a DynamoDB table keyed by your account. Everything is transmitted over HTTPS.
Who can see it
Cosydays does not sell your data, share it with advertisers, or run any analytics or tracking on you. There are no third-party trackers in the app or on this site.
Your data reaches exactly three places beyond our own storage:
- Octopus Energy, when Cosydays reads your account or sends a control command you asked for.
- Anthropic, through AWS Bedrock, when you ask for an AI analysis. What is sent is the daily figures for the period you chose — energy, heat, COP, cost, temperatures — and your question. Your name, email, address, account number and API key are not part of it.
- Sentry, if error reporting is switched on for the deployment you are using. Errors are scrubbed before they are sent, personally-identifying data is switched off, and session replay and screenshots are deliberately disabled — a screenshot of this app would be a photograph of your credentials.
Similar Homes is opt-in, and coarse on purpose
Comparing your home against others means contributing to that comparison, so it is off until you turn it on, and you can turn it off again at any time.
What is contributed is your energy and efficiency figures against a cohort key — a coarse description of your home, never an identifier for it. Where an area is used it is the postcode district only, such as SW1A. A full postcode is refused rather than shortened, because accepting one would mean it had already been sent, logged and stored before anything trimmed it. Cohorts below a minimum size return no answer at all rather than one that could be traced to a household.
How long it is kept
Readings are kept while your account exists, because the point of the app is the comparison across seasons and years — a history deleted after ninety days cannot answer "is this winter better than last".
Getting rid of it
- Disconnect your Octopus account (Settings → Octopus connection). Your API key is deleted and collection stops immediately. Readings already collected are kept, so your history survives a reconnection — the app says so before you confirm.
- Leave Similar Homes (Settings → Similar homes). Your contribution is withdrawn. This is never behind a paywall.
- Delete everything (Settings → Account → Delete account). Your account, every reading collected under it and every sign-in attached to it are removed. It happens immediately and it cannot be undone.
Your rights
Under UK GDPR you can ask for a copy of what we hold, ask for it to be corrected, or ask for it to be deleted. Email hello@cosydays.co.uk and we will respond within a month.
Changes to this page
If what Cosydays does with your data changes, this page changes with it and the date at the top moves. A change that widens what is collected or where it goes will be announced in the app rather than made quietly.