DarkWatt – Privacy Policy

Last updated: 2025-07-13

Thank you for installing DarkWatt.

Your privacy is central to the way we designed the extension.

This document explains:

what data DarkWatt collects
why it is collected
where and how it is stored
the choices you have

DarkWatt never transmits raw browsing data, screenshots, or any other personal information to our servers (we do not even operate servers). All processing stays on your device.

1 . What data does DarkWatt collect?

Category	Details	Where stored	Retention
Web history	- URL, page title, time of visit	IndexedDB inside the browser profile	Until you delete the data or uninstall the extension
Website content (screenshots)	A down-sampled (32 × 32 px) bitmap of the visible tab	Only in RAM for < 100 ms while brightness is computed	Discarded immediately after calculation
Derived metrics	- average luminance per sample CPU usage fraction

calculated watt-hours saved | IndexedDB inside the browser profile | Until you delete the data or uninstall the extension |

2 . Why is the data collected?

Purpose	Data needed	Justification (Chrome policy § 3.1 “necessary for primary purpose”)
Estimate display energy	down-sampled screenshot → luminance	Required to compute how “dark” the page is
Attribute energy to a site	URL, title, timestamp	Lets you see per-site savings in the leaderboard
Compare CPU vs display load	CPU usage fraction	Part of the “energy per tab” feature set

3 . How is the data processed?

Every 5 s (configurable) DarkWatt
- captures the visible tab (chrome.tabs.captureVisibleTab) only if you have granted the optional tabs permission OR are using the default DOM-sampling mode
- scales the image to 32 × 32 px in an off-screen canvas
- sends the pixel buffer to a sandboxed WebAssembly (WASM) module that outputs a single number: average luminance
The raw bitmap is then discarded.
The luminance, URL, and CPU figures are merged into a per-site energy ledger saved in IndexedDB.