prefer the ones made by 'Voltstick'. ive got a black one where the end lights up red and a green one where it lights up fred and buzzes.
ive had the black one for 10 years, still going strong.
Volt Stick ::: The market leading brand in AC, DC voltage and megnetic testers in the UK
I carry a MK volt-stick, the type with the variable sensitivity control which is less prone to false positive indications.
Show off !fluke ldv2 got a torch on it as well, quite good and 2 tools in 1
I carry a pair of snips 100% effective at detecting live wires!!!!!! and usually have the added bonus of tripping the circuit without need to trace it.