The small silvery ball in a mercury thermometer can be dangerous if the glass breaks and the mercury is not cleaned up properly. The mercury will evaporate and can contaminate the surrounding air and become toxic to you and your family. Occasionally serious illness and even death results may occur from exposure to mercury from fever thermometers.
However, if the consumer fails to clean up mercury either because he or she is unaware that it has broken or because it is difficult to gain access to the mercury (for instance because it has seeped through a carpet), then the mercury will might reach dangerous levels in indoor air. The risks increase if the consumer attempts to clean up a mercury spill with a vacuum cleaner, or if the mercury is heated for some reason. The danger of significant mercury exposure is greatest in a small, poorly-ventilated room.
Never use a vacuum cleaner as they do not pick up the drops and vacuuming vaporises the mercury.
Never use a broom as this breaks up the mercury further
Never pour it down the drain as this blocks the sink and harms the waterways
Never wash clothing with mercury split on it as this will contaminate the washing machine and spread it, dispose of such clothing.
To prevent possible contamination, stop using your mercury thermometer. Get a new, safer type of thermometer.