Event technology

Radio controls won’t flatten your SIAC

Many organisers limit radio controls to protect competitors’ SIAC batteries. We worked out what turning on “Send last record” really costs. It’s about 0.2% of a SIAC’s battery life where radios are listening, about 1% at worst, and nothing at all for the controls.

Tate Needham

meshO · 8 October 2026 · 8 min read

A competitor with a SIAC on their finger reaches over a control. A meshO Control radio unit with an antenna is mounted on the control beside the SPORTident unit. — A contactless punch at a control fitted with a meshO Control radio unit. Photo: meshO

At the recent Oceania carnival, only some of our controls were set up as radio controls. The reason was one we hear often: a worry that asking every SIAC to radio its punches would run competitors’ batteries flat. SIACs aren’t cheap, and no organiser wants to be blamed for a flat battery.

So we worked out what it actually costs. The answer is hardly anything. Turning on “Send last record” at every control shortens a SIAC’s battery life by about 0.2% when radio receivers are listening, and by about 1% in the worst case, where there are no receivers out at all. It makes no difference to the controls. That means organisers can switch it on everywhere and put radios wherever they’re needed on the day.

How a contactless punch works

When you punch with a SIAC in AIR+ (contactless) mode, the control isn’t reading your card. It works the other way round. A control in beacon mode keeps sending out a short-range signal that reaches about 30 to 50 cm. That signal carries the control’s number and a few settings. When your SIAC passes through it, the SIAC saves the punch in its own memory, then flashes and beeps to tell you it worked.

The control never hears from your SIAC. It doesn’t know you were there, and it doesn’t keep a record of your punch. Your SIAC holds the only copy until you download at the finish.

Where radio controls come in

Every SIAC also has a small built-in radio, which SPORTident calls Short Range Radio, or SRR. It uses the same licence-free 2.4 GHz band as Wi-Fi and Bluetooth, and reaches up to about 8 metres.

“Send last record” is a setting on the control. meshO Manager calls the same setting “Send the last punch”, under AIR+ radio. When it’s switched on, the control adds one extra instruction to the signal it already sends: once you’ve saved this punch, send it by radio. Your SIAC then sends a short radio message with your card number, the control number and the time.

If a radio receiver is set up near the control, it hears the message, replies with a quick “got it”, and passes the punch on to the arena for live results, commentary or the big screen. The SIAC hears the reply and stops.

If no reply comes back, the SIAC tries again, switching between its two radio channels: red, blue, red, blue, red, blue. After six tries it gives up. Either way, your punch is already saved on your SIAC. The radio message is only an early copy for the people at the arena.

How a radio control works. 1: the control sends its number and the Send last record setting to the SIAC, one way, over 30 to 50 cm. 2: the SIAC saves the punch, beeps and flashes. 3: the SIAC radios the card, control and time to a receiver within about 8 metres. 4: the receiver replies got it, and the SIAC stops sending. 5: the receiver passes the punch to the event arena. With no receiver nearby, the SIAC tries six times, alternating red and blue, then stops, and the punch is still saved on the SIAC. — **Figure 1. How a radio control works.** The numbered steps follow one punch. The control only ever sends, so “Send last record” adds nothing to its workload. The SIAC saves the punch first and sends the radio message second, so a missing receiver never costs a competitor their punch.

Close-up of a SPORTident control unit numbered 112 on its bracket, with a meshO Control radio unit clipped on below it, above the orange and white flag. — A meshO Control radio receiver clipped on beside the SPORTident unit at control 112. With “Send last record” on at every control, a receiver can be added to any control on the day. Photo: meshO

Competitors in a marquee in the event arena looking at screens of live results. — Competitors check live results in the arena. Radio punches put splits on the screens while runners are still on course. Photo: meshO

What it costs the SIAC

Each radio message takes about a thousandth of a second to send. Add the time to wake the radio and listen for a reply, and each try keeps the radio busy for about five thousandths of a second.

To see what that adds up to, we took a keen orienteer: two courses a week, 20 controls each, every week for five years. That’s about 10,400 punches. A SIAC battery holds 140 mAh and lasts about five years at that rate of use.

With a receiver at every control, each punch needs one radio message. Over five years that adds up to about one minute of radio time. The battery goes flat about 3.5 days sooner, a 0.19% reduction in battery life.

With no receivers anywhere, every punch uses all six tries. That’s about five minutes of radio over five years. The battery goes flat about three weeks sooner, a 1.1% reduction.

Those days aren’t extra time the SIAC spends switched on. They’re how much earlier the battery runs flat, at the end of five years.

SIAC battery life over five years of keen orienteering

“Send last record” off

5.00 years
baseline

On, receiver at every control

4.99 years
0.19% shorter, about 3.5 days

On, no receivers anywhere

4.94 years
1.1% shorter, about 3 weeks

Battery life Life lost to radio messages, drawn to scale

Figure 2. Battery life with and without “Send last record”. The orange slivers at the ends of the bars are the battery life lost to radio messages. With receivers at every control, it’s about one pixel wide.

Over five years, the extra radio time adds up to about one minute.

Most orienteers punch far fewer controls than our keen orienteer, so their share is smaller still. To put the numbers in context, SPORTident notes that SIAC batteries rarely last much beyond five years however they’re used, because the cells age. And the three rounds of beeps that confirm each punch go on for more than a second, while the radio message is over in a few thousandths of a second.

What it costs the control

Nothing. “Send last record” is one more bit in the signal the control already sends to every SIAC that passes. The control doesn’t listen for radio messages, send anything extra or do any extra processing, so its battery lasts exactly as long with the setting on as with it off.

Running a control in beacon mode does use more of its battery than direct punching. That’s the same whether “Send last record” is on or off.

Our advice: switch it on at every control

When you program controls for an event, turn on “Send last record” (“Send the last punch” in meshO Manager) at all of them, not only the ones you plan to use as radio controls. Then:

You can add a radio receiver at any control during the event, without collecting the control to reprogram it.
You can move receivers when plans change, for a new spectator control, an extra commentary split or a control you want to keep an eye on.
Controls without a receiver work exactly as before. Competitors won’t notice anything, and their punches are saved on their SIACs as usual.

In the worst case, it costs a keen orienteer’s SIAC about three weeks over five years. In return, every control on your course is ready to become a radio control whenever you need one.

How we worked it out

Usage: 2 courses a week with 20 controls each, so 40 punches a week and 2,080 a year. SIAC switched on about 2 hours a week, every week for 5 years.
Battery: 140 mAh at 3 V, lasting 5 years at that use, which is about 28 mAh a year.
Radio: each message is 36 bytes sent at 250 kbit/s, which takes 1.15 ms. The SIAC waits about 3 ms for a reply and tries up to 6 times, alternating red and blue.
Charge per try: about 92 microcoulombs (0.026 µAh) to wake the radio, send and listen, from datasheets and testing.
Battery life: 140 mAh ÷ (28 mAh a year + the extra radio use per year).
Blue-only receivers: a receiver that listens only on blue misses the first (red) try, so each punch takes two tries. That’s about 0.4%, or a week sooner. Receivers that listen on both channels catch the first try.

Sources: SPORTident user guide and SIAC documentation (docs.sportident.com); ACT Orienteering, “Everything You Need to Know About SPORTident AIR+” (act.orienteering.asn.au).