Hook: Wall Medium (Blue Square)The Coil Monitor decoration fits into a blue medium square wall hook.
Hook: Wall Large (Purple Rectangle)The Coil Monitor decoration fits into a large purple rectangle wall hook.
How to Get a Coil Monitor Decoration
Cartel Pack Decorations
The Coil Monitor decoration can be dropped from Vigilant Defender Packs, which were released on the Cartel Market and bought with Cartel Coins. Cartel Packs, including the Vigilant Defender Pack, include a random selection of items from the Vigilant Defender collection of items. You aren't guaranteed to get a Coil Monitor decoration from a Vigilant Defender Pack, but it is one of the few ways to get a Coil Monitor deco apart from buying it on the GTN from another player.
If you're looking to get a Coil Monitor, the easiest way to get it is to head to the Galactic Trade Network (GTN) in SWTOR and buy it with credits from another player. If it's very rare and not available on the Cartel Market, you could try buying from the GTN and hope you get it.