Which of the following is a possible cause of an alarm system drawing excessively on the power supply?

The correct choice is touchscreen keypads, as they often have higher power demands compared to traditional keypad systems. Touchscreen interfaces typically require more energy to operate due to their more advanced technology, which includes features such as backlighting and graphics display. When multiple touchscreen keypads are integrated into an alarm system, they can significantly increase the overall power draw, potentially leading to issues with the system's power supply if it's not adequately supported.

While old wiring can lead to resistance and potential power loss, it doesn't inherently increase the power draw of the system itself. Low batteries would typically signal a lack of available power, rather than an excess draw. Excessive weather conditions may affect the performance of the system, but they do not directly cause an increase in the system's power requirements in the manner that advanced touchscreen technology does.