docs: point at FCC internal photos for checking a PCB before opening it

components/levoit/README.md

@@ -19,6 +19,10 @@ humidifiers (Superior 6000S), enabling local control without cloud dependency.
 ### Hardware Setup
 
 - ⚠️ Requires disassembly and serial access (TX, RX, GND, EN, GPIO0) initially
+- 💡 Before opening anything, the FCC filing for most Levoit models includes
+  **internal photos of the bare PCB** — browse grantee
+  [`2ARBY`](https://fccid.io/2ARBY) (Arovast Corporation) to find yours and
+  see the module and test pads in advance
 
 
 #### Option 1: Flash Original ESP32 Directly

devices/README.md

@@ -100,6 +100,16 @@ Choose the approach that fits your device and risk tolerance:
   - Cleanest for long-term custom firmware; cannot easily revert to stock without rework.
 
 General tips:
+- **Look at the board before opening it.** Levoit's FCC filings are under
+  grantee [`2ARBY`](https://fccid.io/2ARBY) (Arovast Corporation) and most
+  include internal photos of the bare PCB — enough to spot the Wi-Fi module
+  and the test pads. Examples:
+  [Core 200S](https://fccid.io/2ARBY-CORE-200S) ·
+  [Core 300S](https://fccid.io/2ARBY-CORE-300S) ·
+  [Core 600S](https://fccid.io/2ARBY-CORE600S) ·
+  [Sprout](https://fccid.io/2ARBY-B381S). Note the hyphenation is
+  inconsistent (`CORE-300S` but `CORE600S`), so browse the grantee index
+  rather than guessing an ID.
 - Backup with `esptool read_flash 0 ALL levoit.bin` if possible.
 - Common wiring: 3V3, GND, TX→MCU RX, RX→MCU TX, EN, GPIO0 (for boot).
 - For WiFi LED/filter LED behaviors and entity list, see the component README.

docs/adding-a-new-device.md

@@ -39,8 +39,42 @@ still welcome, just a different shape (see the 🔴 *Custom HW* rows in the READ
 table).
 
 Record what you find: board photos, chip markings, and any FCC ID on the module.
-An FCC ID gets you [internal photos and test reports](https://fccid.io), which
-often answer questions without further disassembly.
+
+### Check the PCB before you open anything
+
+Anything sold in the US with a radio in it has an FCC filing, and those filings
+usually include **internal photos** — the manufacturer's own pictures of the
+bare board. That is often enough to answer the ESP32-plus-MCU question, spot the
+Wi-Fi module and see where the test pads are, *before* you buy a device or take
+one apart.
+
+Search [fccid.io](https://fccid.io) for the ID printed on the device's rating
+label, or browse by manufacturer:
+
+| Grantee | Maker | Covers |
+|---------|-------|--------|
+| [`2ARBY`](https://fccid.io/2ARBY) | Arovast Corporation | **Levoit** / VeSync — purifiers *and* humidifiers |
+| [`P53`](https://fccid.io/P53) | MXCHIP | The Wi-Fi modules Philips uses, e.g. [`P53-EMC6069`](https://fccid.io/P53-EMC6069) |
+
+Known Levoit filings, as examples of the naming:
+
+| Device | FCC ID |
+|--------|--------|
+| Core 200S | [`2ARBY-CORE-200S`](https://fccid.io/2ARBY-CORE-200S) |
+| Core 300S | [`2ARBY-CORE-300S`](https://fccid.io/2ARBY-CORE-300S) |
+| Core 600S | [`2ARBY-CORE600S`](https://fccid.io/2ARBY-CORE600S) |
+| Sprout | [`2ARBY-B381S`](https://fccid.io/2ARBY-B381S) |
+| Dual 200S humidifier | [`2ARBY-DUAL200S`](https://fccid.io/2ARBY-DUAL200S) |
+| OasisMist LV450S / LV600S | [`2ARBY-LV450S`](https://fccid.io/2ARBY-LV450S) · [`2ARBY-LV600S`](https://fccid.io/2ARBY-LV600S) |
+
+Note the inconsistent hyphenation — `CORE-300S` but `CORE600S` — so don't guess
+an ID from the model name; use the [grantee index](https://fccid.io/2ARBY).
+
+Two caveats. Internal photos are sometimes held under **short-term
+confidentiality** and only appear months after the grant date, and schematics
+and block diagrams are almost always permanently confidential — the Philips
+AC2889 filing is an example. And the photographed revision may not match the
+unit in your hands. Treat them as reconnaissance, not ground truth.
 
 ## 2. Identify the UART pins and capture dumps