I've been encountering this question more frequently lately.
Having a lockbox installed is an important part of the selling process. A lockbox provides agents with easy access to the property when the owner is not home to personally open the door for prospective buyers. It’s the industry norm for allowing convenient showing times.
The combination to the lockbox is only released to registered agents VIA their brokerage for added security. All buyers are escorted by their agent during showings, and never passed on to the public.
If you’re uneasy about the use of a lockbox, consider removing the keys at night after all the showings are complete for the day. Just be sure to replace the keys in the morning! You may also want to consider changing the combination on a regular basis for added security.