diff --git a/main.c b/main.c
index 4a9287d..1132cd4 100644
--- a/main.c
+++ b/main.c
@@ -42,6 +42,9 @@ static volatile uint16_t shake_count = 0;
 // number of time counts (+1 @ 488 Hz)
 static volatile uint32_t time_count = 0;
 
+// time after last shake to go to sleep, in seconds
+#define REST_TIME (5 * 60U)
+
 // blocking wait (in 10 us steps, up to UINT32_MAX / 10)
 static void wait_10us(uint32_t us10)
 {
@@ -254,9 +257,10 @@ void main(void)
 			puts("\r\n");
 			shake_count = 0; // reset count
 		}
-		if (time_count > 488 * 10) {
-			puts("10s\r\n");
+		if (time_count > 488UL * REST_TIME) {
+			puts("rest\r\n");
 			time_count = 0; // reset counter
+			LED_UV_PORT->ODR.reg &= ~LED_UV_PIN; // switch UV LED off
 			led_red(0); // ensure LED is off
 			led_green(0); // ensure LED is off
 			led_blue(0); // ensure LED is off
@@ -283,7 +287,7 @@ void shake_isr(void) __interrupt(SHAKE_IRQ)
 	shake_count++; // register vibration
 }
 
-// time counter
+// system time counter
 void time_isr(void) __interrupt(IRQ_TIM4)
 {
 	TIM4->SR.fields.UIF = 0; // clear flag