If you use these under the blankets at night, I have it on good authority that you will go blind.
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: 15mm x 31mm x 14mm (approx.) Weight per cufflink: approx. 13g (heavy)