Ultimately surveillance is about using ears and eyes to gather information about a possible enemy and your surroundings, to get forewarning, to give you the largest tactical advantage, to plan an ambush or evacuate with as much warning as possible.
Extending coverage of these senses gives a longer warning, and more time for reacting to, or preparing for, a security threat.
In a scenario where our security is left up to ourselves (Without rule of law or WROL) we need to find ways to extend these warnings as far a possible.
Each scenario you could plan for is unique, but there a few things that can be taken as a given for all places surveillance is required.
To begin with the best types of surveillance are those that require no power and are as simple as your own two eyes.
Start with a good pair of field glasses, or a good rifle scope.
Night vision ,and super hearing amplifiers are great for night time.
Alternatively use the ears of a well trained dog.
Trip wires and traps, should be used to multiply force, even if its just to make a big noise for the dog to hear , or for you to see.
Drones are one of the first things that spring to mind when talking about surveillance in a modern context, but drones are by no means the only type of surveillance you should have,
most people think of Drones as noisy quad-copters with cameras that can keep an eye on your property.
But there are other types that you can employ that can help with surveillance and counter-surveillance.
Flying UAV are a great part of a surveillance system, but lack the sustained flight that a good surveillance needs, Rolling drones are a better idea for longer battery life these are really just mobile moving cameras.
Closed circuit Camera’s and other electronic devices are all great but require tech , power and repairs, and you still have to man them for them to be any good.
For longer range consider a Marine radar AS IT can be used to track movements and pick up on intruders up to 5 km away.
In conclusion it would recommend a few well trained dogs .. and a good pair of field glasses as a bare minimum. with Listening posts and watch towers.
if you alone or in a really small group then electronic means can be used as a force multiplier in the short term, but long term installations require man power and these require getting together.
Radio nets and field telephones are a great way to relay info in this way and share surveillance – as part of knowing a head is getting reports from others, never underestimate the need to share and help those around you .. they can provide huge amounts of indirect information and warning.