Summary

Kamstrup energy meters can be read using an optical protocol. This is a reading head to hold two IR LEDs in place, that can be 3D-printed.

Instructions

Detailed instructions (in danish): http://wiki.hal9k.dk/projects/kamstrup

Manufacture the PCB using the included original Kicad sources (kamstrup-v2.zip), OR the eagle version by @boelle (eagle-kamstrup-by-boelle.zip).
3d-print the enclosure. The holes will probably need to be drilled to correct diameter for a snug fit: use a 5mm drill for the two LED holes, and a 6mm drill for the magnet holes. You might need to scale the lid a bit for a tight fit.
The enclosure has 4 holes in the bottom, in which 4 magnets will fit, e.g. http://www.supermagnete.de/eng/S-06-06-N . These hold the enclosure unto the metal-ring found on some Kamstrup meters.

Kamstrup DIY Energymeter