There are three main sorts now. The traditional cast iron bed with rubber pad holding the glass reflectors, stick on reflective studs ( now mainly used for temporary works as it was found as sson as anything hit them, they became unstuck reflective studs!) and solar LED cats eye, which charge up from solar power and then stay on permanently through the night (bit unnerving when you first see them in your mirrors!). These are quite expensive (£54 ea I think), so when I'm working on road works replacing the tarmac, they have a crew with a corer that cuts them out first. They then have to be sent away to have the surrounding tarmac taken off them!