Hi there,
Welcome ā¦Back. 
So, what have YOU tried first ? Post what code you have tried, and one quick note, You are asking for one answer to two different power modes, and that is where the confusion starts.
Sure I could post some code but that isnāt really going to help you., Iām a āTeach a man to Fishā kind of contributorā¦
Understand the finest points, I have extracted from the Low Power 
ninja @msfujinoās threadsā¦and
these are the results with nordic AI sprinkled in for clarity and background.
For the nRF52840, the deepest sleep is System OFF. Nordic lists that at about 0.40 ĀµA for the SoC with no RAM retention, wake on reset. But in System OFF, the LFCLK is off, so the internal RTC cannot keep running to wake the chip later. System OFF wake is for things like GPIO DETECT and reset-type wake sources, not the internal RTC. 
So the straight answer is:
- Accelerometer interrupt wakeup in the lowest-current mode: yes, that is possible, because the IMU can assert an interrupt onto a GPIO and wake the nRF52840 from System OFF via a pin sense/DETECT event.
- RTC interrupt wakeup from that same deepest mode: not with the internal nRF52840 RTC. If you insist on timed wake while staying in the deepest mode, you need an external RTC/alarm output wired to a GPIO wake pin.
If you need both:
- wake on motion
- wake on time
- and do it with the internal RTC
then you should use System ON sleep, not System OFF. Nordicās numbers for the SoC are about 3.16 ĀµA in System ON, full RAM retention, wake on RTC with LFRC. Real XIAO BLE Sense board current will be higher than that because it is a board, not a bare chip, and because the IMU must remain powered/configured enough to generate its interrupt. 
The architecture choice
Option A: lowest possible current
- nRF52840 in System OFF
- IMU left running in its own low-power interrupt mode
- IMU INT pin wired to a GPIO wake pin on the XIAO
- wake only on motion
- no internal RTC timed wake in this mode
Option B: timed wake + motion wake
- nRF52840 in System ON sleep
- internal RTC running
- GPIO interrupt from IMU also enabled
- current higher than System OFF, but this is the only way to get both using the internal RTC
Option C: lowest current + timed wake
- nRF52840 in System OFF
- use an external RTC/alarm chip to pull a GPIO and wake it
- IMU interrupt can share the same wake strategy on another GPIO
So the real design choice is:
- Lowest current: System OFF + IMU interrupt wake
- Time + motion wake: System ON sleep + RTC + IMU GPIO wake
- Lowest current + timed wake: external RTC alarm into a GPIO, not the internal RTC
I would decide that first, then write the code. 
I could not promise a single magic number like āX ĀµA with accel + RTC wakeā for the XIAO BLE Sense. The chip floor and the board floor are not the same thing, and the IMU mode matters a lot. The LSM6DS3 family can run in low-power modes, but the exact total depends on:
- IMU ODR
- which interrupt feature is enabled
- pullups and stray wiring
- onboard peripherals and bootloader behavior
- how the board is powered and measured
here is a couple skeletons to look at and try assuming the IMU interrupt line is already configured and connected to a wake-capable GPIO:
#include <Arduino.h>
#include <Adafruit_TinyUSB.h>
#include "nrf_gpio.h"
#include "nrf_power.h"
#define IMU_INT_PIN D2 // example only
void setup() {
pinMode(IMU_INT_PIN, INPUT_PULLUP);
// Configure wake on pin state change using SENSE
nrf_gpio_cfg_sense_input(
g_ADigitalPinMap[IMU_INT_PIN],
NRF_GPIO_PIN_PULLUP,
NRF_GPIO_PIN_SENSE_LOW // or HIGH, depends on your IMU interrupt polarity
);
delay(10);
// Enter System OFF
NRF_POWER->SYSTEMOFF = 1;
}
void loop() {
}
That will wake by reset-like restart, so setup runs again after wake. That is how System OFF behaves on nRF52 Arduino cores too.
Internal timed wake: System ON sleep, RTC/timer style
For internal timed wake, stay in System ON and use a low-power timer/RTC-driven schedule instead of System OFF:
#include <Arduino.h>
volatile bool wakeFlag = false;
void rtcCallback() {
wakeFlag = true;
}
void setup() {
// configure low-power timer/RTC here
// configure IMU interrupt pin here
}
void loop() {
if (wakeFlag) {
wakeFlag = false;
// read IMU / do work
}
// sleep CPU, keep RTC alive
__WFE();
}
btw, That is the right shape for āwake by time and by GPIO,ā but it is not the absolute lowest-current state. YMMV 
Pick any two of those with the internal peripherals.
If you want all three, add an external RTC/alarm. 
HTH
GL 
PJ
Real , running code for ALL of the above descriptions and explanations are in The examples I have posted on here along with videoās I might addā¦
my Link Spoon 
is Broken, I have OpenClaw agents fixing it Now. 
At least that is consistent with the higher readings when it was wired. But why? 
PJ 