It is a very good idea that someone should know where you are. However, even if a security buddy knows where you are, if you get a stroke or heart attack you may not want to wait some time until they notice, or rely on them to figure out what happened and then call 999.
It can be life saving to educate yourself about the symptoms so that you can take immediate direct action if possible. Have 999 saved on your phone(s), and possibly even have a note of your address on the phone so that you can read it out in case you are struggling to think and communicate. I don't know if 999 can track a mobile's location, it'd be great if it can.
It may be even better to register with emergencySMS, have a draft SMS with all the information needed, and text it to 999 as soon as you notice the symptoms.
There are also some apps that claim to be able to call emergency services and send an automated text with your location. Never used any so can't tell how well they actually work. With emergencySMS there should be no need to use them, they might be more useful if you are travelling abroad.