Touching the sensor bar shouldn't be a problem at all. The sensor bar itself is actually a very low tech peice of equipment, simply 2 infrared LED bulbs on either side, powered via the connection to the nindendo Wii. Fingerprints directly on the infrared parts (the black glossy plastic parts on either side of the bar) can effect the performance of the sensor bar, just like when you put your hand in front of the TV remote (which works the same way) and the buttons no longer work. If there are fingerprints on the infrared parts, simply use a gentle cloth to wipe them off, I promise you that if fingerprints get on it, there will be no perminant damage and once the fingerprints are clear, the sensor bar will work fine again. The same can be said for the tip of the wiimote. If it gets smudged or dirty, clean it with a gentle dry cloth and it will be back to 100% function.