So, my idea is simple;
if someone has a mod installed that adds power, all these devices (Lasers, scanners, electrified fences) require power. Elsewhise, they don't. (A config option enables "classic behaviour" which removes the need for power, ever). Fences, when damaging players, use "x" amount of power per injury.

Also, if you do such a thing, fence's should form a "network" with other fences they touch. a fence controller can be placed on it, and that controller will allow you to say who can and can't touch it.

The doors will let anyone through without power, keypads won't open, locking you, and so on! So, be careful, lest you get locked in your base!

I generally like the idea, though we need to see how best to display and configure power requirements, especially when there are no mods installed that can generate power. SecurityCraft is not supposed to be a power generator mod, and considering how many SecurityCraft appliances a base could potentially have, such power generation would need to have the capabilities to be very powerful (pun not intended), which inherently makes SecurityCraft a viable source for power. That is unintentional, hence we won't add means for power generation.
Having said that, there is no way we can reliably check if there are mods installed that add power generators, so enabling power usage for SecurityCraft's blocks would likely require turning on a setting in the config. This can be confusing to players who think that they can feed power to SecurityCraft's blocks, while they actually can't. Similarly, players who have the config setting enabled, but don't have a mod installed that can generate power, will be confused as to why their blocks aren't working.

Well, what if you implement the need for power but don't add any power generation? there are a lot of mods out there that don't exactly add a power generation to be used along with their blocks/entities.

Or do add a power generation, but not really strong, just a initial source of energy that doesn't really help much when your base starts to grow a lot, but having in mind that normally you wouldn't play with only one mod, you'll have other mods for power generation and storage.

I've seen mods such as Draconic Evolution that requires tons and tons of energy not having a reliable power generation (*besides the draconic reactor which honestly isn't really "reliable" either), just a simple initial power generation.

I think the Infinity Generators from Lucraft: Core would be perfect to suit the power requirements.