Owain

That may vary widely depending on DVR. Always best to use relays with decent isolation.

or you could use an ethernet controlled mains switch; it would have different software from your cctv viewer. They're used in server farms to remotely power-cycle servers. http://www.audon.co.uk/lanpower.html http://www.lindy-usa.com/power/remote-switching.html

Most PTZ protocols have Aux commands, which you can use to control lights with a RS422/485 telemetry receiver and relays. Something like http://www.bbvcctv.com/products/receivers/rx25x_multiple_protocol_auxiliary_relay_receiver/ A more DIY approach http://www.sigma-shop.com/category/17/rs485-relays.html

Why don't you get a large lockable box that UPS can put your parcels into?