Ambient room light power source
This shows a way to the get enough power to run a very low powered device using just ambient room light. It is a low power solar USB charger. It produces 5.5v and 360mA in full sunlight but the panel will also produce some electrical energy even in dim light. I bought this through a USA outlet called ‘The Electronic Goldmine’. They also ship to most countries in Europe. Most small usb solar chargers sold worldwide might also work.