Hi Ling,
Pls don't get offended. I'm just giving my opinion only. No hard feelings. In fact, most of the shops at Sim Lim Square do sell dummy camera for less than $10.
I normally do not post but because you mention something that I did not share the same opinion, that's why I wrote in. Honestly speaking, depends on what the mummy here wants, most of them (in my opinion) want to install the camera so that they can monitor what is going on at home when they are working outside. In short, they want to have a peace of mind especially if they have a maid looking after the baby.
Most of the CCTV now will enable the parents to view what is going on at home online. They do not need to go home and rewind and watch the video again.
In my opinion, a dummy might be beneficial only if you install it outside your house to scare strangers away.
As I have said, no hard feelings, just different opinion. I really don't think it's a waste of money to install a CCTV if you really have a need especially if you want to monitor on your maid with you baby. By the way, not all CCTV cost few thousands. You can get most CCTV with less than 1K.