I think you will find that brake pad sensors are not generally clever electronic sensors in the conventional sense. Rather a termination of two wires embedded in the pad such that when the pad has worn down to reveal the "sensor", the two wire terminations complete a circuit across the disc surface and hence light the dash warning.
On this basis, if the dash warning light has illuminated, it's time to change. Pull a wheel off and by looking through the front of the caliper, you will see the amount of friction material left. It's not that expensive or difficult a job to do yourself if you are slightly mechanically minded. I would regard it as the easiest of the non routine service jobs. However, as MikeM says, don't leave it too long.
Might be worth a visit to E Car Parts on Ebay, sensors about ?7.50 or 15 for front and back. They're a lump of plastic that eventually gets mashed by the worn pad, 24K sounds low, it might be worth jacking up, removing front wheel and checking it - you can see the sensor + pad thickness quite clearly through the caliper. The very thin wires can get cut quite easily if the little plastic ties fail that hold them to suspension .