Miners lamp cufflinks - lights up with a red light when the black button on the back is pressed. Not sure if the red light could have another use or meaning - I'll leave it up to you.
The round back of these cufflinks contains the battery - it does not remove to go through the sleeve (unscrewing it will reveal the wires). The thickness of it does mean you need to firmly push it through the button hole and may make it unsuitable for shirts with smaller holes.
Dimensions: 26mm x 15mm x 15 mm (approx.) Weight per cufflink: approx. 11g (heavy)
Size = x mm (W x H)