Old wiring is not automatically dangerous, and new wiring is not automatically safe. What matters is the type, its condition, and whether anyone has modified it badly.
Here is how to identify what is actually in your walls.
Knob and tube
Ceramic knobs holding single conductors, ceramic tubes where wires pass through framing, and no ground conductor at all. Common in homes built before about 1945.
In pristine condition and never modified, knob and tube can still function. That is almost never what we find. The insulation embrittles, the system has no ground, and it must never be buried in insulation. Most importantly, decades of additions are usually spliced into it with no junction boxes.
It should be replaced, and it is often the reason an insurer asks questions.
Cloth and rubber sheathed cable
Post-war through the 1950s and 60s. Looks like a fabric-wrapped cable. The rubber insulation underneath hardens, cracks and falls away, particularly where it enters hot fixture boxes.
The classic symptom is a ceiling fixture where the conductors are bare for the last inch. Tug the wire and the insulation flakes. Once that starts, the cable is at the end of its life.
Aluminium branch circuits
Roughly 1965 to 1974. Solid aluminium conductors on 15 and 20 amp branch circuits, marked AL on the cable jacket. Aluminium expands and contracts more than copper, which loosens terminations over time, and it oxidises into a poorly conducting film.
Remediation does not always mean rewiring. Approved connectors used to pigtail copper tails at every device and splice are an accepted repair. What is not acceptable is leaving aluminium terminated directly on standard devices.
Two prong outlets and missing grounds
A two prong outlet means no equipment ground. Replacing it with a three prong outlet without running a ground is the single most common unsafe DIY change we find, because it tells every future occupant the circuit is grounded when it is not.
The correct options are to run a ground, or to fit GFCI protection and label the outlets as having no equipment ground.
Do you have to rewire everything at once?
Rarely. A staged plan usually starts with the panel and service, then the circuits serving kitchens, baths and outdoor areas, then bedrooms and living spaces. Open walls during a remodel are always the cheapest moment to do a section.
What we would not stage is anything showing heat damage, exposed conductors or a fault. That part comes out first.