A surge suppressor (sometimes optimistically called a “surge protector”) is a device inserted in the alternating current (AC) utility line and/or telephone line to prevent damage to electronic equipment from voltage “spikes” called transients. A more accurate term for this type of device is “transient suppressor.” A typical surge suppressor is a small box with several utility outlets, a power switch, and a 3-wire cord for plugging into a wall outlet.

Surge suppressors probably can not guarantee no damage on a massive lightning strike. For a surge suppressor to  work properly you need to make sure you have 3 prong plug and wiring. The three prong has a ground that is necessary for it too work.

UL advises the more money you spend, generally the better quality you get. That being said, even the cheapest ones offer decent protection. Make sure you see a UL symbol on the suppressor.

For treadmill users what kind of surge protectors (expense level) should be  considered safe?A treadmill should probably have at least 1,000 joules of protection. That would cost about $30-50, but thats a small price to pay to protect your investment in a treadmill..