Those devices, the ones with a reader on your arm, all have a small needle. The are "less invasive" in that you don't need to prick your finger 5 times a day. But they still need to break the skin to get a blood measurement. There is so far nothing that can read blood sugar from either photo or electric sensors.
They're called continuous monitoring systems, or CGM. The insert has a patch over it, with a small transmitter. So the insert can be on your upper arm, and the device it transmits to can be in your pocket, on your belt, or an arm band. But you have to carry something. CGM can be enhanced by interacting with an insulin pump, a similar device attached to the body with an insert that contains insulin which it can release as needed. This is more for Type I diabetes, were people use insulin most. Insurance coverage is another factor on all of this: good old fashion strips and finger pricks are the cheapest tech, and accurate enough to get the job done. Cost is key for insurance plans, and decisions are made based on fractions of pennies.
Newer tech is to use a smart phone to replace a separate CGM monitor, or even an insulin pump monitor. I'm not sure how far along that is. Pharma companies tend to want to keep their system like these closed, not open architecture, or interchangeable parts, so people have to buy into the whole system. That kind of thinking leads to slow development, and often inferior tech in some areas since pharma companies are not experts in apps and smart devices.
It has been said, going back 10 years ago at least, that Apple, Samsung, Sony, etc have secret think-tanks, and are pouring serious R&D, and are including clothing and accessory companies, like Nike, Levies, and some up-start pharma device companies, on wearable and implants, for a variety of health monitoring products that are integrated into all kinds of things we normally wear.
Non-invasive is best, and that is also cutting edge R&D. I recall hearing, at least 10 years ago, that R&D on reading glucose through the skin surface, has lead to prototypes. It's only a matter of time before that hits the market. Question would be how accurate; might be for Type II's only.
It won't be too long before wearable and implanted devices continuously monitor all kinds of health issues, from pacemakers to insulin pumps, and dozens of other things, feeding into via our smart phones ... and watches ... directly to our doctors. That info could be called up by emergency responders, at hospitals, etc when needed.
There's huge R&D on systems to pull all that data together going on now.