The purpose of this study is to gather feedback on a new continuous glucose monitor (CGM), called DEXCOM One. Unlike some other CGMs which allow a low (hypoglycaemic) and a high (hyperglycaemic) glucose alarm to be set, the DEXCOM One sensor has the unique feature of the 'Sustained Hyperglycaemic Alert', where the alarm is only activated if the glucose is above a certain threshold for a pre-specified amount of time.

International consensus guidance states that people with diabetes should aim for 70% time in the range 3.9-10 mmol/L. After meals there is usually a rise in blood glucose, so it is not unexpected for the glucose to go above 10 mmol/L for a short time even if the insulin dose already given before a meal is correct. Therefore, people with a high glucose alarm set at 10 mmol/L on their GCM may unnecessarily inject extra insulin and risk a low blood glucose. However, DEXCOM One's Sustained Hyperglycaemic Alert would only notify patients if their blood sugar was high for a prolonged period, and so may reflect a time when it would be genuinely advantageous to inject more insulin.

The aim of this single-centre, non-randomised, observational study is to gather experience from a range of users to assess the utility of this unique attribute, and the optimal settings. We aim to recruit 80-100 patients, and each participant's involvement is in 2 phases; for the first 3 months DEXCOM One sensors will be used, and for months 4-6 there will be the option of continuing to use the DEXCOM One sensors with the addition of a FitBit to track physical activity.

Inclusion Criteria:

• Aged 18+ years
• A patient registered in the diabetes service at Sheffield Teaching Hospitals NHS Foundation Trust
• HbA1c within the last 3 months of >70 mmol/mol

Exclusion Criteria:

• Unable to provide informed consent
• Unable to communicate in written and verbal English