A wearable external defibrillator comprising: a first patient engagement substrate comprising: one or more sensing electrodes configured to engage with a patient's skin to detect a cardiac signal; a defibrillator electrode pad configured to engage with the patient's skin and to deliver an electrical therapy to the patient, the defibrillator electrode pad configured to be in continuous electrical communication with the patient's skin; and an elastic element configured to conform to, and stretch with, the patient's skin to allow the wearable external defibrillator to be worn continuously during movement and showering activities; a battery; an electrical energy source including one or more capacitors; a second patient engagement substrate comprising: a second defibrillator electrode pad; an adhesive; and a second plurality of sensing electrodes, the second defibrillator electrode pad configured to engage with the patient's skin and to deliver an electrical therapy to the patient, the second defibrillator electrode pad configured to be in continuous electrical communication with the patient's skin, the second defibrillator electrode pad in electrical communication with the electrical energy source; a controller configured to detect the cardiac signal with the sensing electrodes and to deliver a therapeutic shock through the defibrillator electrode pads to the patient while the patient engagement substrates are engaged with the patient, wherein the controller is configured to charge the one or more capacitors with the battery and to discharge the one or more capacitors through the defibrillator electrode pad of the first patient engagement substrate and the second defibrillator electrode pad; two or more separate housings connected to the first patient engagement substrate and enclosing the battery, the one or more capacitors, and the controller; and a support layer configured to engage with and support the controller, the one or more capacitors, and the battery. a first patient engagement substrate comprising: one or more sensing electrodes configured to engage with a patient's skin to detect a cardiac signal; a defibrillator electrode pad configured to engage with the patient's skin and to deliver an electrical therapy to the patient, the defibrillator electrode pad configured to be in continuous electrical communication with the patient's skin; and an elastic element configured to conform to, and stretch with, the patient's skin to allow the wearable external defibrillator to be worn continuously during movement and showering activities; one or more sensing electrodes configured to engage with a patient's skin to detect a cardiac signal; a defibrillator electrode pad configured to engage with the patient's skin and to deliver an electrical therapy to the patient, the defibrillator electrode pad configured to be in continuous electrical communication with the patient's skin; and an elastic element configured to conform to, and stretch with, the patient's skin to allow the wearable external defibrillator to be worn continuously during movement and showering activities; a battery; an electrical energy source including one or more capacitors; a second patient engagement substrate comprising: a second defibrillator electrode pad; an adhesive; and a second plurality of sensing electrodes, the second defibrillator electrode pad configured to engage with the patient's skin and to deliver an electrical therapy to the patient, the second defibrillator electrode pad configured to be in continuous electrical communication with the patient's skin, the second defibrillator electrode pad in electrical communication with the electrical energy source; a second defibrillator electrode pad; an adhesive; and a second plurality of sensing electrodes, the second defibrillator electrode pad configured to engage with the patient's skin and to deliver an electrical therapy to the patient, the second defibrillator electrode pad configured to be in continuous electrical communication with the patient's skin, the second defibrillator electrode pad in electrical communication with the electrical energy source; a controller configured to detect the cardiac signal with the sensing electrodes and to deliver a therapeutic shock through the defibrillator electrode pads to the patient while the patient engagement substrates are engaged with the patient, wherein the controller is configured to charge the one or more capacitors with the battery and to discharge the one or more capacitors through the defibrillator electrode pad of the first patient engagement substrate and the second defibrillator electrode pad; two or more separate housings connected to the first patient engagement substrate and enclosing the battery, the one or more capacitors, and the controller; and a support layer configured to engage with and support the controller, the one or more capacitors, and the battery.