Spot: an electricity spot price traffic light
Spot shows with a coloured LED ring whether electricity is cheap, average or expensive right now. The display shows the current spot price and the time until the price changes.
- Works with Home Assistant
- Open source
- No cloud
A pre-order costs nothing. You pay after we e-mail you that your device from the first batch is ready to ship, and you can cancel until then.
Illustration of use. Photos will follow from the first batch. See the enclosure
How it works and how it connects
- A ring of 12 LEDs shows the electricity price by colour; the display is the other part of the head.
- The ring plugs in with a keyed 6-pin JST-PH connector, the display with a Qwiic cable.
- Inside the box is the Jádro board, powered over USB-C 5 V from an adapter; the ring does not light up on battery.
- It gets the price over WiFi from Home Assistant at home, and downloads it from the internet when Home Assistant is not running.
- On green you start the washing machine or dishwasher, and an automation can switch on the water heater.
What it will look like
3D design of the enclosure, which you can also print yourself. The product is not manufactured yet, the design may change after the first test prints.
Connect to Home Assistant in three steps
Plug it in
Put Spot where people will see it, such as the kitchen or next to the washing machine, and power it over USB-C.
Set up WiFi over Improv
Over a USB-C cable from your browser, or over Bluetooth from Home Assistant, where you confirm the pairing by pressing the BOOT button. Once connected, Spot fetches prices for today and tomorrow.
Connect it to Home Assistant
Adopt Spot through the ESPHome integration. If you already have an OTE spot price integration, Spot uses its prices. Colour thresholds are regular number entities.
Why a traffic light
On a dynamic tariff the price of electricity changes throughout the day. It tends to be lower at night and often around midday when solar output is high, and higher in the morning and evening. Day-ahead prices are published in advance, so you can plan, but nobody wants to open an app every time they start the dishwasher.
Spot sits on a shelf and shows with its ring whether power is cheap (green), average (yellow) or expensive (red). The OLED shows the exact price and how long until it changes. Everyone in the house gets it, including the people who will never open Home Assistant.
Where the prices come from
If you run Home Assistant with an integration for OTE spot prices (for example a custom integration from HACS), Spot uses its data, so the light matches what your automations see. If you do not have Home Assistant or it is down, Spot fetches the day-ahead prices itself. All it needs is WiFi.
Since October 2025 the day-ahead market trades in 15-minute blocks, so Spot counts down to the end of the current block, not just the hour.
What you control from Home Assistant
The colour thresholds are plain number entities. Some people like fixed values, others recalculate them daily from the average price. Spot also exposes its state as an entity, so you can hang more automations on it, for example turning on the water heater on green.
Open and cloud free
No cloud, no app. Firmware is ESPHome under MIT, schematics under CERN-OHL-P-2.0. Want the ring to show solar production or home battery charge instead? Change the config and push it over the air.
Spot costs 990 CZK, is available for pre-order and ships to Czechia and Slovakia via Packeta once the first batch is produced.
What is in the box
- Jádro in a PETG enclosure with a printed lid
- 12-LED WS2812 ring and 1.3 inch OLED display
- Link to the manual and source files
Specifications
| Product code | PR-SPOT |
|---|---|
| Indicator | 12-LED WS2812 ring: green, yellow, red |
| Display | 1.3 inch OLED, SH1106 controller |
| Shown on display | current price, time until the price block changes |
| Price source | any OTE spot price integration in Home Assistant, fallback: fetches day-ahead prices itself |
| Thresholds | set from Home Assistant |
| Standalone mode | yes, without Home Assistant |
| Power | USB-C 5 V |
| Chip | ESP32-C6-WROOM-1 (WiFi 6, BLE, Thread) |
| Firmware | ESPHome, MIT licence |
| Enclosure | printed PETG |
| Warranty | 24 months |
| Price | 990 CZK |
FAQ
Is it only for the Czech market?
The built-in fallback fetches Czech day-ahead prices from OTE. With Home Assistant, Spot can show any price entity you give it, so it can follow another market if you have an integration for it.
Does it show the final price including grid fees?
By default it shows the day-ahead energy price. If you calculate your final price including fees in Home Assistant, Spot can display that instead.
How do the thresholds work?
Two number entities in Home Assistant: green below the lower one, red above the upper one, yellow in between. You can change them with automations too.
Does it handle 15-minute prices?
Yes. The European day-ahead market moved to 15-minute intervals on 1 October 2025 and Spot counts down to the end of the current block.
Do you ship outside the Czech Republic?
We ship to Czechia and Slovakia via Packeta. For other EU countries, e-mail us at info@plosnaryba.cz and we will find a way. Prices are in Czech koruna (CZK).
When will it ship?
Spot is on pre-order and ships once the first production batch is made.
Docs and source files
Device documentation · Firmware from the browser · How it works
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