If you look to protect your lone workers, the sensible application of technology can be a useful part of an overall policy towards protecting (and abiding by your duty of care for) lone workers.
Even more important however is how your staff interact with their environment when alone. The greatest technology is not going to make the decision for you as to whether you enter a house unaccompanied or how to respond to the question just put to you by the curious looking character in front of you - who is now blocking your only means of escape......
Look for an organisation that does much more than risk assess and take an interest in not just selling you technology, but how to make the best use of it. For example which way should you throw the attractive (firm's) phone that the mugger wants?
Be safe
TheMADMAXMAN