Transcutaneous analyte sensor

1. A transcutaneous system for measuring an analyte concentration in a host, the system comprising:

a sensor adapted for transcutaneous insertion through a skin of a host;

a subassembly comprising a mounting unit adapted for placement adjacent to the skin of the host and an electronics unit configured to be releasably attachable to the mounting unit, wherein the subassembly is configured such that the mounting unit and the electronics unit are located over an exit site of the sensor when the sensor is inserted through the skin of the host; and

an applicator comprising a needle comprising a lumen, wherein the needle is configured to receive the sensor, wherein the applicator comprises a plunger configured to push the needle and the sensor through the mounting unit and subsequently retract the needle into the applicator, thereby leaving the sensor in the host.

2. The system of claim 1 , wherein the needle surrounds the sensor.

3. The system of claim 1 , wherein the plunger irreversibly retracts the needle into the applicator.

4. The system of claim 1 , wherein the system is configured to insert the sensor through the skin with a depth to about 2 cm.

5. The system of claim 1 , wherein the system is configured to insert the sensor through the skin with a depth of from about 0.1 mm to about 2 cm.

6. The system of claim 1 , further comprising a component configured to maintain the sensor at a predetermined depth in the host upon retraction of the needle into the applicator.

7. The system of claim 6 wherein the component is configured to maintain the sensor at the predetermined depth in the host upon irreversible retraction of the needle into the applicator.

8. The system of claim 1 , wherein the applicator is configured to insert the sensor in response to an activation of an automated mechanism.

9. The system of claim 1 , wherein the applicator is configured to insert the sensor in response to a manual force applied to the applicator by a user.

10. An applicator system for inserting a transcutaneous sensor into a host, the applicator comprising:

a sensor configured for transcutaneous placement through a skin of a host;

a needle comprising a lumen, wherein the needle is configured for inserting the sensor into the host, wherein the sensor is disposed in the needle prior to insertion into the host;

a subassembly comprising a housing adapted for placement adjacent to the skin of the host and an electronics unit releasably attachable to the housing; and

an applicator configured for inserting the needle and the sensor into the skin of the host, wherein the needle and the sensor are disposed within the applicator prior to insertion of the sensor;

wherein the applicator is configured to insert the needle and the sensor into the skin of the host to leave the sensor transcutaneously placed within the host, and

wherein the applicator is configured such that it must be released from the housing in order to allow the electronics unit to be attached to the housing.

11. The system of claim 10 , wherein the sensor is disposed in the lumen of the needle.

12. The system of claim 10 , wherein the sensor is disposed within the lumen of the needle.

13. The system of claim 10 , wherein the sensor is disposed within the needle.

14. The system of claim 10 , wherein the applicator is configured to insert the sensor in response to an activation of an automated mechanism.

15. The system of claim 10 , wherein the applicator is configured to insert the sensor in response to a manual force applied to the applicator by a user.

16. The system of claim 10 , wherein of the applicator is configured to release from the housing after the sensor has been transcutaneously inserted into the host.

17. The system of claim 10 , wherein the applicator is releasably attached to the housing prior to sensor insertion and during sensor insertion.