Reservoir with low volume sensor

1. A medical device for administering liquid drug therapy to a user with a low volume sensor, said medical device comprising:

a flexible reservoir for containing a supply of a liquid drug;

a rigid structure with a chamber and a side hole in fluid communication with the flexible reservoir;

a plunger mounted inside the chamber and configured to seal one side of the chamber; and

a sensor for detecting low liquid volume in the flexible reservoir, wherein:

when the inside end of the plunger passes the side hole, the sensor is activated to transmit a signal indicating low liquid volume in the flexible reservoir.

2. The medical device of claim 1 , wherein the sensor comprises an electrical switch.

3. The medical device of claim 2 , wherein the electrical switch is triggered by a button.

4. The medical device of claim 1 , wherein the sensor comprises an optical sensor.

5. The medical device of claim 1 , wherein the sensor comprises a magnetic sensor.

6. The medical device of claim 1 , further comprising a control module connected to the sensor for receiving the low liquid volume signal.

7. The medical device of claim 1 , further comprising an alarm system for warning of a low liquid volume state of the reservoir.

8. The medical device of claim 7 , wherein the alarm system transmits a light signal as a warning of low liquid volume in the reservoir.

9. The medical device of claim 7 , wherein the alarm system transmits sound signal as a warning of low liquid volume in the reservoir.

10. The medical device of claim 7 , wherein the alarm system transmits a vibrational signal as a warning of low liquid volume in the reservoir.

11. The medical device of claim 7 , wherein the alarm system transmits a combined light, sound and/or vibration signal as a warning of low liquid volume in the reservoir.

12. The medical device of claim 1 , further comprising a pump mechanism for pumping liquid out of the flexible reservoir.

13. A medical device for administering liquid drug therapy to a user with a liquid volume sensor, said medical device comprising:

a flexible reservoir for containing liquid;

a pump mechanism in fluid connection with the flexible reservoir for pumping liquid out of the flexible reservoir;

a freely movable plunger in fluid communication with the flexible reservoir and the pump mechanism, the freely movable plunger moving only in response to liquid pressure and not forming a part of the pump mechanism;

a sensor for detecting liquid volume inside the flexible reservoir by detecting a position or change in position of the freely movable plunger; and

a control module in functional connection with the sensor for receiving a volume signal from the sensor.

14. A method for detecting low liquid volume and notifying a user of time-to-empty in a system comprising a pump mechanism, a flexible reservoir for housing a supply of a liquid drug, a rigid structure with a chamber and a side hole in fluid communication with the flexible reservoir, a plunger mounted inside the chamber and configured to seal one side of the chamber, a sensor for detecting low liquid volume in the flexible reservoir, and a control module in functional connection with the pump mechanism for controlling the operation of the pump mechanism, wherein when the inside end of the plunger passes the side hole, the sensor is activated to transmit a signal indicating low liquid volume in the flexible reservoir, the method comprising the steps of:

providing the rigid structure with the chamber connected to the flexible reservoir;

applying a negative pressure to end of the rigid structure;

removing fluid from the flexible reservoir;

detecting moment that the plunger loses contact with the sensor;

calculating estimated time for empty based on current flow rate and volume of the chamber and the conduit;

alerting the user that volume is low; and

notifying user of an approximate time when the system will run out of liquid.