Not sure about this particular device, but https://citylabs.net/technology-overview/ https://citylabs.net/technology-overview/ apparently makes use of tritium,

Not sure about this particular device, but https://citylabs.net/technology-overview/ https://citylabs.net/technology-overview/ apparently makes use of tritium, which is betavoltaic based. Just noticed for citylabs it says - "Base price starts at $5,250 per battery" I'm curious what they'd be used for considering the very low power output and cost.