Red Laser Pen

To help with this you do not have to keep your finger on the button.

Once pressed the pen will stay on until the button in pressed again. 

This inexpensive and lightweight laser pen is useful for ray optics demonstrations and simple diffraction work. 

Power: 0.5 milliwatts

In addition to this you can make your point on overhead images with this useful presentation tool.

Caution: Laser Light. Do not stare into the beam or view directly with optical instruments.