Finds and permissions log for detectorists

The idea

Detectorists run a three-part memory problem: what they found, where exactly they found it, and what they agreed with the landowner. All three live in WhatsApp threads, camera rolls, and glove boxes. In the UK the stakes are concrete: detecting without documented permission is trespass at best, and Treasure Act finds demand a paper trail.

Every hobby app in this space is a finds gallery. The wedge is making the permission the organising object: terms, expiry, a photo of the signed form, and a drawn boundary, with finds and coverage mapped inside it. Expiry warnings and a coverage heat layer answer the two questions every detectorist has before a weekend: where am I still allowed, and where have I not been.

Who pays

The buyer owns a 300 to 2,500 dollar machine and treats permissions as their scarcest asset; 25 dollars a year to protect and organise them is easy. UK detectorists are the beachhead because record-keeping is quasi-compulsory there. Distribution: massive detecting Facebook groups, YouTube dig channels, and metal detecting clubs whose committees would promote anything that keeps members compliant with landowners.

MVP scope

• Permission records with terms, expiry alerts, signed-form photo, and drawn map boundary
• Offline find logging with photos, category, depth, and automatic GPS-to-permission assignment
• Map view with find pins and a per-permission coverage heat trail
• CSV plus photo export per permission
• Skip for v1: find identification via AI, social sharing feeds, club multi-user features, US federal land rules

Build GroundTruth, a React Native (Expo) logbook for metal detectorists where Permissions are a first-class object, not an afterthought.

Permission record: landowner name and contact, free-text terms (finds split, access days, crops to avoid), start and expiry dates, a photo of the signed permission form, and a boundary drawn on the map (polygon tool in Mapbox). The app warns 30 days before a permission expires and shows an expired badge on its pins. UK-focused framing: this doubles as the legal paper trail detectorists are supposed to keep.

Find logging: from the field, tap Log Find, take 1-3 photos, pick a category (coin, artefact, jewellery, button, relic, junk), optional ID notes and depth. GPS pin attaches automatically and the find is assigned to whichever permission polygon contains it (or Unassigned). Works fully offline with sync later; fields have no signal.

Coverage layer: record a breadcrumb GPS trail while detecting (background location, batched to save battery) and render it as a translucent heat layer per permission, so hunted ground versus untouched ground is obvious at a glance.

Screens: Map (pins, boundaries, coverage toggle), Find log, Finds gallery with filters, Permissions list and detail, Export (CSV plus photos ZIP per permission, useful for finds-split conversations and Treasure Act reporting).

Stack: Mapbox for maps and polygons, Supabase for auth/sync/storage. Pricing: free for 1 permission and 25 finds; 25 dollars per year unlimited.