The BRIGHT Study (Device Name: HALO System)

Inclusion Criteria: * Willing to sign an informed consent form * Age ≥ 18 years * Willing to comply to study protocol requirements (study visits with frequent venous blood sampling and deliberate insulin, glucose, ketone and lactate challenges) * Willing to charge the SENSOR on daily basis * Willing not to insert their standard CGM and/or insulin pump in and around the SENSOR implant site (± radius 5 cm)\[TS\| XR1.1\] Diagnosed with type 1 diabetes mellitus according to the World Health Organization criteria, for at least 12 months prior to screening, on CSII therapy Exclusion Criteria: * Known allergy to polydimethylsiloxane (PDMS) * A contraindication to undergo challenging tests (i.e., ischemic heart disease, epilepsy, panhypopituitarism, hypoadrenalism, untreated hypothyroidism) * History of hepatitis C or HIV or other disease transmissible by blood * A condition requiring or likely to require magnetic resonance imaging during the study duration * Female participants who are pregnant, planning on becoming pregnant or nursing * Coagulation disorder, wound healing and bleeding disorder or taking anticoagulant medication (oral anticoagulants; antiplatelets (such as aspirin, ticagrelor are allowed). * Anemia identified by a haemoglobin \<14 g/dL for men or \<12 g/dL for women * The presence of any other active implanted device * The presence of any other CGM sensor/pump located in the lower abdomen (other location is acceptable) * Waist circumference of \>120 cm * Any disorder, which in the investigator's opinion might jeopardise participants' safety or compliance with the protocol.