My Solonese friend who is a high silat master was teached this ability to detect "empowered" blades. For this he would pass his hand along the blade close to it but without touching it and feel a vibration or rather tingling feeling as said by Mick. I tried it but it was not very successful probably by lack of relaxation and training (although I have dowser abilities which may help). An alternative technique which he uses is to hold a match and pass it along and close to the blade for transmitting the feeling to the hand. Try it yourself!
Regards